docs(guide): Talk about removing unused features (#16085)

### What does this PR try to resolve?

Helps users find ways to identify unused features in dependencies.

This also pulls in
- General improvements from #15991 (in particular, the grouping of links
with content since this was going to make it worse)
- Review feedback from #16078

### How to test and review this PR?

Author: weihanglo

src/doc/src/guide/build-performance.md

@@ -122,8 +122,26 @@ Recommendation: Periodically review unused dependencies for removal using third-
 When changing code,
 it can be easy to miss that a dependency is no longer used and can be removed.
 
-> *Note:* native support for this in Cargo is being tracked in [#15813](https://github.com/rust-lang/cargo/issues/15813).
+> **Note:** native support for this in Cargo is being tracked in [#15813](https://github.com/rust-lang/cargo/issues/15813).
 
 Trade-offs:
 - ✅ Faster full build and link times
 - ❌ May incorrectly flag dependencies as unused or miss some
+
+### Removing unused features from dependencies
+
+Recommendation: Periodically review unused features from dependencies for removal using third-party tools like
+[cargo-features-manager](https://crates.io/crates/cargo-features-manager),
+[cargo-unused-features](https://crates.io/crates/cargo-unused-features).
+
+When changing code,
+it can be easy to miss that a dependency's feature is no longer used and can be removed.
+This can reduce the number of transitive dependencies being built or
+reduce the amount of code within a crate being built.
+When removing features, extra caution is needed because features
+may also be used for desired behavior or performance changes
+which may not always be obvious from compiling or testing.
+
+Trade-offs:
+- ✅ Faster full build and link times
+- ❌ May incorrectly flag features as unused