This. USE flags are the real strength of Gentoo. There can be benefits with various C(XX)FLAGS, LDFLAGS, etc. However, most of the time^1^ those changes are at best moderate, and sometimes outright dangerous.

With Gentoo, if $PKG has a choice to require $LIBKITCHENSINK, you can choose not to. This, sometimes, can mean saving a TON of compile time. Also, the kernel is arguable more secure^2^.

1. One time I recompiled either Opera, or some lib it depended on with some magic LDFLAGS and got a notable speedup on startup. However, this is fairly rare.
2. IIRC, a certain part of the kernel can rerandomize the kernel stack in memory, meaning that, unlike a Debian kernel or Fedora kernel, no one can be entirely sure what a certain data structure would be in memory.