Cargo workspaces are more of an optimization in that they let all the crates in your project share the same output directory[0], so built dependencies can be shared among every crate, as opposed to each crate needing to (re)build all of its dependencies independently.

This helps to reduce compile times when working on projects where you frequently switch between crates.

[0] https://doc.rust-lang.org/book/ch14-03-cargo-workspaces.html