I use them a bit at my work and the main reason is to reduce how much I’m fetching (which can take a couple of minutes). It’s also good for avoiding accidental inconsistencies between copies (Git will complain if you try to check out the same branch in MyProj and AltMyProj if they are both worktrees). You can checkout the same commit in two worktrees though so you can still do it in practice if really necessary.