Are we talking about `cargo build` here? Because my understanding is that if a lockfile is present and `Cargo.toml` hasn't changed since the lockfile was created then the build is guaranteed to use the versions in the lockfile.
If however `Cargo.toml` has changed then `cargo build` will have to recalculate the lockfile. Hence why it can be useful to be explicit about `cargo build --locked`.
If however `Cargo.toml` has changed then `cargo build` will have to recalculate the lockfile. Hence why it can be useful to be explicit about `cargo build --locked`.