Here's one tiny example:
Want to link a static library that is also built from rust code? Yeah, you can make that work somehow by spawning another cargo from build.rs. Oh, you wanted to do that in a workspace? Ah no sorry, cargo is going to dead lock.
The locking is super frustrating, I have cargo & rust-analyzer wrestle for it all the time, and my hacky solution for it so engrained that I just forgot it even happens until you mentioned.
Corollary of my example: when some hacky things rely on cargo to work (like some crate that does magic by using the output of cargo metadata (that actually exists, IIRC, or if not exactly that, something along those lines)), you better hope that the crate using those hacky things doesn't end up in your dependencies when you're using a workspace.
