As seen in the https://rust.godbolt.org/z/Y8djWsq1P - write! macro produces significantly more code than a write_str call, so this change should have somewhat better performance. To my knowledge, a lot of ppl tried to solve this optimization in the compiler, but no luck yet, so may help compiler ourselves for now.
To keep with DRY principle, I think it makes it a bit less redundant to reuse the Self::<associated_type_name> structure in the well known trait implementations - keeps it consistent with the trait decl too.
Yuri Astrakhan