Tangentially related: the opposite, Rust's borrow checker sans the compiler, is actually very useful. As far as I understand, the borrow checker is a significant part of the work of writing a Rust compiler. Therefore, having the official borrow checker available as a standalone program can make alternative compilers (e.g. for exotic hardware) feasible faster, because they won't need a borrow checker of their own from the get-go.
I get your point, but still you haven't identified a use for the borrow checker sans the compiler.
Why would this matter? The borrowck is (a) not needed during bring-up because as its name suggests it is merely a check, so going without it just means you can write nonsense and then unbounded undefined behaviour results, but (b) written entirely in Rust so you can just compile it with the rest of this "exotic hardware" Rust compiler you've built.