It gives you access to 100% of Linux's system calls. It eliminates a lot of global state. It gets rid of a lot of legacy C library crap.

Years ago I wrote a rationale for such a thing in my liblinux project:

https://github.com/matheusmoreira/liblinux/blob/master/READM...

I don't maintain it anymore because nolibc is better but there's a lot of references in that text if you'd like to read them.