But what is the actual benefit of these decluttering applications, if we now exclude, for example, the complete removal of an application from the computer?
In my view; there are none, except for perhaps the fuzzy feeling you might get thinking; that feels good, my mac will probably work just a little better now. Which is BS. As mentioned, caches are there to make things work better, and chances are that you risk cleaning up something that is needed, and screw up stuff. I'd never trust these "CleanMy-" apps to delete files from my computer.
I'm sure I have lots of redundant files from old apps lying around, but I'm also sure that they take up a miniscule amount of disk space, and that they don't affect functionality in any way.
The only thing you might call an exception to this approach is that I have some things excluded from backup, including the Caches folder in /Library. It will rebuild after a restore from backup.