Without it, nobody on the management side of things actually writes any code, or has first-hand experience with working on the product. The line managers just end up as a go-between between the workers and their directors, because they only know what their reports tell them. They don't know much for themselves.
You can't quantify this sort of loss on an earnings report, but among many other things, it does a great job of diluting ownership of the product away from the teams working on it.
I have a lot of thoughts on this. IMHO, it's appropriate for the state that Google is in now, where it is a large mature conglomerate, basically finance & managerially driven, built around optimizing 10-K reports and exec headcount & control. It's not a particularly good move from the perspective of shipping great software, but Google doesn't really do that anymore.
The reason is because software construction and management is unintuitive, and concrete details of implementation very often bubble up into the architecture, team structure, and project assignments required to build the software. TLM-led teams have a very tight feedback loop between engineering realities and managerial decisions. Your manager is sitting beside you in the trenches, they are writing code, and when something goes wrong, they know exactly what and why and can adopt the plan appropriately. Most importantly, they can feed that knowledge of the codebase into the new plan. So you end up with a team structure that actually reflects how the codebase works, engineers with deep expertise in their area that can quickly make changes, and management that is nimble enough to adopt the organization to engineering realities rather than trying to shoehorn engineering realities into the existing org structure.
Now, as an EM with 10+ reports, I'm too far removed from the technical details to do anything other than rely on what my reports tell me. My job is to take a slide deck from a PM with 10 gripes about our current product, parcel it out into 10 projects for 10 engineers, and then keep them happy and productive while they go implement the mock. It will take them forever because our codebase is complex, and they will heroically reproduce the mock (but only the mock, because there is little room for judgment calls in say resize behavior or interactivity or interactions with other features and nobody's holding them accountable for things that management didn't have time or bandwidth to ask for) with some hideously contorted code that make the codebase even more complex but is the best they can do because the person who actually needed to rewrite their code to make it simple reports up through a different VP. But that's okay, because the level of management above me doesn't have time to check the technical details either, and likewise for the level of management above them, and if it takes forever we can just request more headcount to deal with the lack of velocity. Not our money, and it's really our only means of professional advancement now that product quality is impossible and doesn't matter anyway.
Ultimately the value of the TLM role was in that tight bidirectional feedback between code, engineers, and management. As a TLM, you can make org-structure decisions based on what the code tells you. As an EM, you make org-structure decisions based on what your manager tells you. But at some point in a company's lifetime, the code becomes irrelevant - nobody reads it all anyway - and the only thing that matters is your manager's opinion, and by transitivity, your VP's opinion. A flattened org structure with as many reports per manager as possible is a way for the VP to exert maximal control over the largest possible organization, mathematically, and so once that is all that matters, that is the structure you get.
As far as I can tell, the main function of an EM is to enforce the company policy. I'm not sure there really is a need at a smaller place.
In a small company (let's say anything under Dunbar's Number), you have a very dense network organically, and EM's aren't necessary. As the company grows larger, the matrix becomes sparser and sparser- until you get to something like Google (180k employees plus maybe that many again contractors) and you have almost all 0's. So an EM's job is to solve the communication problem, because information still needs to flow around the company, in and out, whether it's "do this project" or "another team already solved this problem" or "this project is a never-ending world of pain and should be ended" to "employee 24601 is awesome and should be given more responsibility."
Probably the best description I've heard of the EM role is that "It's a large collection of part-time roles, all with disparate skillsets, that together are responsible for ensuring the success of the project."
Communication is a huge part of that - downwards (telling reports the information they need to be successful), sideway (getting information from cross-functional partners and managerial peers so you align your projects with theirs), and upwards (managing expectations and asking for direction at the appropriate point so upper management doesn't freak out).
But other skillsets involved are: playing therapist (managing anxiety, morale issues, resentment, and misconduct); coaching (both technical and interpersonal); splitting up vague exec mandates into subgoals; prioritizing; hiring; managing performance; serving as a point of contact for whatever random problems your reports bring you; negotiating; setting team structure; developing expertise among your reports; managing their careers so they get promoted; ensuring that they're recognized for their accomplishments; helping people have fun in the office; modeling a culture of respect; selling new product initiatives; and yes, enforcing company policy.
I find that it works well, the TLM keep a foot in the action, so to speak and has a better idea of what's happening with the product being developed, what issues we're facing (also in terms of tools, environments...) and it keeps their knowledge of the product more up to date. Of course with their background, I wouldn't say they are all the greatest at managing, but I don't think they've ever done big mistake on that side of their role. So in short in our case it works, but it could just be a consequence of the local organisation and people working there.
I thought it was a nice stepping stone for people to learn management without having 10 people dumped on them. But it looked bad on paper.
Once you're late stage though, that's done. TLMs are probably being held to 100% of IC standards and manager standards, people under them are jockeying for "impact" and don't want to compete with their manager, etc.
I totally see why it wouldn't work at today's Google. Honestly maybe it's a positive sign they recognized that.
There’s always a downside to anything, and the merits/demerits are all about the politics of the org.
I really never intended to have a management position, but this has been an incredible opportunity to experience a portion of it without fully committing. Other replies have described this as a transitional role, and I don't think they're wrong. In the long term, especially if the company grows, I can probably be more valuable by committing to one path or the other. However, for the right person and situation, I could see us minting a TLM again, regardless of size.
Simple as that. It’s fine during times of growth but that’s not happening right now.