It's a good idea when you're working with small changes. If I'm working on fixing some bug, it should probably be in one-commit and done. But sometimes you're working on a bunch of "testing123" "save where I'm at" commits - and you don't want those in the end.

And then if you're working on a larger feature, you have that feature branch and make these small one-commit merges into that branch. When you merge that larger feature - it'd be great not to squash those commits.