What is the advantage of using worktrees over another checkout in another folder?
When you're done working in a separately cloned repository in another folder, if you're anything like me, before deleting it (via `rm -rf`) you'll want to check very carefully for additional branches, unpushed work, anything stashed. Deleting an entire repository that's been around for a while is a risky operation in that it may have accumulated other unrelated work in addition to the current branch (which was the primary reason for the clone), and you'll want to check carefully before deleting the whole lot.
Additional worktrees within the same repository are great for medium-term ephemeral separate strands of work. They can be created and removed without concern.
What’s also great is that you don’t need to do a pull in the other folder. Before I discovered worktree, I had my repository checked out in two places, so was either pulling both constantly, or when I needed the alternate, it was often very far behind and I had to pull a lot.
The great thing about worktrees is that everything local is still available in the worktree and vice-versa, you can even stash push on the one side and pop on the other. You also don’t need to push or pull on either side first.
I have noticed that for submodules, although they share the .git folder, they don’t share references, so you can’t see local branches and stashes between the worktrees, but sub module pulls are still quicker since they share objects so those don’t need re-pulled on the other folder.