There's also a new .sbox folder in your projects for project-specific temporary files and caches (such as cookies, asset thumbnails, and the download cache for cloud assets). Before these files were all stored in a single global folder inside steamapps.
If you're someone who's precious about every last byte of storage, you'll now free more of that up when you delete a project. More practically though, this change will keep things more organised and avoid the unnecessary work we had before with a single global temporary folder for all projects, like often having to redownload cloud assets because the version was different.
If you haven't already, you'll want to add as an exclusion to any existing project repos to keep this out of version control.