They make things so much easier, having to make copies of every layer every time just to keep the original in case you need to re-do something half an hour later is super annoying.
Especially if you do multiple different things with a layer. Do you really have the patience to make backuo copies of a layer after every little edit you apply to it?
And then let’s say step 2 of 5 didn’t turn out like you want. Backup copies or not, you still have to re-do everything from 2 to 5 because of GIMPs destructive nature as of right now