In Build wheel from sdist (optionally?) · Issue #257 · pypa/build · GitHub, we are questioning whether building wheels from sdists, as opposed to the local source directly, should be the recommended behavior.
My opinion is that it should. Building wheels, or other future distributions, from sdists makes it so that things like unchecked files, cache, etc. don’t influence the built wheel. This avoids issues like accidentally including extra source files, and helps with reproducibility.
I believe this behavior should be recommended to users, and that package builders should be recommended to default to it.
Backends should still take steps to prevent such issues, but given we are entering the age of fully interchangeable backends that anyone can roll out, we need to accept that they might not, and try to mitigate issues there.