A commit followed by a reset or commit --amend later is one more step than a worktree --add. Plus there have been lots of times when I've had some changes staged, and some unstaged debugging or experimental changes that I want to make sure not to commit, and thinking about how to pack all that away neatly so I could get back where I was seemed sufficiently obnoxious that I avoided doing whatever would have required a quick branch switch. Worktree would have let me pick up where I left off without having to think about it.