One issue that I've run into is that if you only bind to IPv6 in WSL, then you will only be able to access the service using IPv6 on the Windows side (i.e. ::1 works, but 127.0.0.1 doesn't). OSs usually automatically bind to IPv4 whenever you bind to IPv6, but that's not the case with WSL (actually, it does bind to both, but only inside WSL, not on the Windows end). Lots of programs (like node) bind to IPv6 by default, so this can catch people off guard and they wonder why 127.0.0.1 or localhost isn't working.

Here's the github issue about it: https://github.com/microsoft/WSL/issues/4851