Real benefit. For average users it’s debatable but if you want to exclude certain components or have complex dependencies “just work” without tons of docker images or need bleeding edge performance by tweaking everything, I don’t see any other choice.
Also if you need to seamlessly integrate new projects that don’t provide packages, writing a live ebuild is straight forward and will keep updated from a regular git repo just like any other package.
Want to compile certain stuff with clang and the rest with gcc? Or use libressl instead of openssl? Stuff like that? No problem. Just be aware that you might need to file bug reports if you do exotic stuff because gentoo won’t prevent you from doing stuff nobody did before.
And installing gentoo by going through the install manual step-by-step, is certainly priceless for diving into linux under the hood. It’s a bit like a LFS but without the hassle.