If you aren't spending tech debt, you don't have a sound monetary policy. Zero tech debt is not a healthy goal.
Is it worth implementing a cache layer in a system? One on hand, you have a better system that can handle more load, on the other, you've spent time that could be spent doing something else. Your systems will almost always have limitations, it's important to understand these and communicate them well. Tech debt should be managed so it doesn't tip over and cause issues. Really good devs and dev managers develop the eye to see when that's about to happen and make sure they convince product that you need to pay that down soon.
This isn't a "Tech Debt" thing. This is a feature/scoping thing. Does my system need to handle 1M concurrent users? If so, support that. If not, don't support it.
But we don't need the absurd concept of "Tech Debt" for effective analysis. We can be specific. We can be clear. Does my system need to support low latency in the face of 1M concurrent users? Yes or no. Now proceed.
"Tech Debt" is such a ridiculous dodge to otherwise avoid real analysis, real work, real clarity.
The answer to "Does my system need to handle 1M concurrent users?" could be "Yes", "No", "Not for the foreseeable future" or even "I don't know".
Given that 'debt' is a way to, in effect, allocate (possible) future resources today, it's pretty clear why it's valuable, especially in the face of uncertainty.
That's a given.
You don't need the notion of "Tech Debt" to deal with that.
It is a complete given at any given time, during any given sprint, that all the features in the queue are ASSUMPTIONS.
That's just a tautology.
"Does my system need to handle 1M concurrent users?"
Maybe you answer Yes or maybe you answer No, but you have to answer something to make decisions about the work ahead of you.
The worst possible place is to be in the fuzzy middle saying fuzzy things like Tech Debt and rolling along fuzzily.
Many teams -- especially teams that love this term "Tech Debt" -- do exactly this.
But they are willfully navigating in the dark and "Tech Debt" is just a term that makes one feel psychologically okay with their ignorance.
But it's euphemism, that's all it is. It does not aid in rational navigation.