,,when the borrow checker is too strict for something you want to do''

Most of the times it isn't. Just as an example here's a random part of serde, the high quality serialization library in Rust:

https://github.com/serde-rs/serde/blob/master/serde/src/priv...

The amount of extra automatic memory management is often a good indicator of not well thought out data structures (although of course they are not always needed).