Recently I had to do an update to the underlying environment a codebase ran on. This was a somewhat involved upgrade and took a longer period of time than most of our work usually does. I did it in a separate worktree, so I didn't have to constantly rejuggle the installed dependencies in the project, and could work on two features relatively concurrently

It also provides some utility for comparing the two versions. Nothing you couldn't do other ways, but still useful