It's definitely a tool that must be used carefully, and why informal rules like "features should be strictly additive" exist. I'd say they are very commonly use

It's definitely a tool that must be used carefully, and why informal rules like "features should be strictly additive" exist. I'd say they are very commonly used by large libraries, for example, here's the list of features for Axum, (arguably) Rust's most popular http server: https://docs.rs/axum/latest/axum/#feature-flags https://docs.rs/axum/latest/axum/#feature-flags