I personally encourage friends, especially those that have been at their job for 5+ years to go to interviews for roles they might find interesting, even if they have no plan of leaving their current role. I have been in the industry long enough to see companies cut ties with employees that have been with them for many years. If they are lucky it is not during a mass firing round, but if they are unlucky it is the result of a large firing round or worse yet a recession of some type. Job hunting and interviewing are at the end of the day a type of competition and if you want to be good at it you need to make sure you have practiced. The benefit of this, is if you make a point of going to interviews where you are still curious about the role, you may actually find your an unexpectedly amazing job and you also are more likely to get a much better offer than you ever would when you are actively looking.
Now when I am a hiring manager, I have zero issue if someone comes with the intent of it being a practice interview. Why? Well, my job as a hiring manager is to win over the candidate to the role I am hiring for. It starts with the one on one, to the exercise I give and to the overall process being a nice experience. If I do those things correctly and the candidate is good, then it usually doesn’t matter what their original motive was for interviewing, they walk out of the process saying I want to work with that person and I want that job. I think a lot of companies don’t understand that the candidates are choosing you as much as you are choosing them. At least that is the way it should be.
I’ll be disappointed if I make an offer and find out they leveraged it for a promotion, but usually you don’t have to tell them anything. You can always say you just want more money and every company has a budget.
You can also just keep in touch. Most folks who would make an offer are happy to talk to you again later or even further along in your career.
I now have hired two people who I sent rejections to after four years!
Some folks will frown on this but here is my philosophy: the company holds all the power, this is you as an individual developing an understanding of that system so it’s not at all unfair, since it started unfairly tilted against candidates - not everyone will agree, but the good news is that you won’t have to talk to the people who disagree again.
e.g., I want a job at Facebook, so I'm going to go interview at some random startups first for sharpness.
I haven't heard of anyone actually taking that advice literally and just randomly giving out interviews even when they have no intention of actually moving from their jobs.
> And what if they make an offer?
I guess you choose whether to accept it or not. An offer does not oblige you to accept.
The fact is, they could offer you an amazing package that will change your mind. Or, they could offer you something you expect but know you wouldn't take. Both are OK.
I'd only think of it as a purposeful waste of time if for some reason you absolutely know you cannot take the job, regardless of anything.