Things projects have that beta projects don't:
* No easy way to automatically add issues from a repo to your project. You have to add them one by one, or use the graphql API, which lacks batch operations.
* No issue preview on the board.
Basic feature missing from sheet view:
* You can't sort issues along the dimensions available in a repo's issue tab (e.g. newest, oldest, recently updated).
I thought I must have been missing something, until I realized that github's public roadmap repo itself uses a bot to add issues [0]. There's an issue there listing out the parity items [1], which will be super handy!