Problem

$CARGO_HOME (or ~/.cargo) is commonly described as just a cache. If it's a cache, it should be fine to delete it and exclude it from backups. If I delete ~/.cargo/bin, however, commands will stop working.

From reference/environment-variables.md:

• CARGO_HOME — Cargo maintains a local cache of the registry index and of
  git checkouts of crates. By default these are stored under $HOME/.cargo
  (%USERPROFILE%\.cargo on Windows), but this variable overrides the
  location of this directory. Once a crate is cached it is not removed by the
  clean command.

From guide/cargo-home.md:

The "Cargo home" functions as a download and source cache.
When building a [crate][def-crate], Cargo stores downloaded build dependencies in the Cargo home.

Possible Solution(s)

• If CARGO_HOME is cache, non-cache content should be stored elsewhere
• If CARGO_HOME is not cache, update the documentation and decide where the cache actually should be stored so it can be easily and safely deleted or excluded from backups