When OpenBSD replaced GNU libtool with a home grown perl version, it was so much faster I believe it literally cut days off machine time off a full ports build. For smaller packages, with tiny C files, running libtool.sh takes longer than running the compiler does. The majority of build time for some of those packages is still running configure, testing for things like <stdio.h>, which the package provides no workaround when missing. The OpenBSD project alone has spent years of machine time to running configure and libtool.
As for doing its job well, the failure mode of configure "you can't build this" is abysmal. Just give me a fucking Makefile, I'll fix it myself. I love packages that come with Makefiles that don't work. I pop "-I/usr/local/include" into CFLAGS, run make again, and boom. Done. Trying to do the same with configure? Forget about it. --with-include-dir or whatever doesn't work, because it's really running some bogus test in the background which expects /bin/bash to exist and so on and so forth.