Glossary
Cargo cache
Cargo's local copy of downloaded crates and related git checkouts.
Rust's Cargo fetches crates into a registry directory, commonly ~/.cargo/registry, and may keep git checkouts alongside it. Those files let later builds of any Rust project on the machine skip the download. They are not your source. They can be large if you have built many projects over time.
Disk Housekeeper treats Cargo caches as part of Smart Clean's developer-cache set. A custom CARGO_HOME moves the directory. Read the preview. Removing the cache means the next fetch downloads again. It does not remove the Rust toolchain unless that toolchain's path is what the preview shows, which is a reason to read the path.