(Not Walter but) Self-hosting in a compiler should be done wherever possible - if we ignore that if the compiler self-hosts it becomes it's own test suite (writing tests is good but it's quite difficult to find weird behavioural bugs using unittests if the tests only test one thing at a time) - it makes it so much easier to work on the compiler (For example, the main D compiler can build itself in a second or two on my machine - if I had to cart around some other huge toolchain it would be much slower). Another boon is that, if people who are really good (let's say) Go programmers want to make the Go compiler better they then don't have to try and write go in C++ if the main compiler is written in C++.

Also, it can also be a plan to rush to a MVP, rewrite the MVP in your language and go from there. This has the added benefit of giving you a decent sized program in your language at no extra cost - aside from testing this should make you design a better language as you learn what works at what doesn't in the "real world".

It's not always possible (Please don't write a compiler in Javascript, or even C if possible - pain and lack of abstraction respectively).