Technically it works the mostly the same as multiple repos, but theoretically allows to have something like a bootstrap script with everything self contained in the same repos. Looks like an alternative tradeoff between a monorepos with shared history and multiple repositories.
I use worktree locally so that, for example, I can have my working copy that I am doing development in and then a separate working copy where I can do code review for someone else, without having to interrupt what I am doing in my own worktree.
My own experience is that if you are using branches with radically different content for different purposes in the same tree, it's going to end up a mess at some point. Worktrees, as far as I am aware, do not help with that in any special way.
As far as I know git worktree is just to have different branches of the same repo checked out in different locations. At least, that's the only way I use it (and it's great!). Are you suggesting to have different projects on different branches? So an empty "master", then "project1", "project2" etc. as branches?
It's offtopic because the second worktree has a detached HEAD, so that doesn't help in the case you mention.