[wandernotlost]

> the function was actually last changed in 2016, but someone modified it last month only to revert the change before submitting a PR

I can't think of a specific example from my own history, but something like this is what has happened. A function was changed in order to support a different change elsewhere in the code. That other change was later modified, incompletely, to remove the need to modify the first function, and the change to the first function was subsequently reverted. Down the road, it's discovered that the modification was incomplete, and when reviewing the new code, you wonder, "how could this possibly have ever worked?" The answer is that it didn't, and when it was committed, there was another supporting change that made it work. By erasing the history of that other change, you remove the possibility of discovering the reasoning behind the change and the source of the introduction of a problem.

If I had seen that intermediate state that's been erased, remember it, and try to find it, now I'm being gaslit by source control, because I remember a real change that was there in a commit, but source control now will lie to me and tell me that it never existed.