I am being flippant, but what the user of the compiler uses it for the vast majority of the time is to get feedback on whether they've missed something. The vast majority of the code in the Rust compiler is dedicated to error reporting. Efficiency of the generated code is important, but it is a well explored space. Emitting good diagnostics is hard and unless you make it a priority it will always be subpar. Communicating with the user to help them get to that generated binary is at least as important, and in my eyes it is more important.
I also consider parsing and syntax to be the least interesting part of any language, as it is also a solved problem that requires little effort (modulo malformed code recovery) in both design and implementation when put in contrast with the rest of the compiler's functions and language design space.
I also consider parsing and syntax to be the least interesting part of any language, as it is also a solved problem that requires little effort (modulo malformed code recovery) in both design and implementation when put in contrast with the rest of the compiler's functions and language design space.