A great example by-contrast is the Gentoo distro, which is (or can be) completely source-code based: you compile everything.
Or, Linux From Scratch (LFS), which is
exactly what it says.
When you "compile everything," of course you can tailor your software very exactly for
your CPU-model and all other characteristics of
your machine. But, it takes time. Sometimes hours. Therefore, it's far more common for someone
else to have compiled the material, using "typical" options, and to then make available the compiled outputs ... the binaries ... which you then install on your machine.
I would, by the way, strongly encourage you to look into both Gentoo and LFS ... perhaps do LFS, in a virtual machine of course, strictly as the learning exercise. You'll learn a
lot. You'll become a more effective user of those binary-only distros because you'll know a lot more about how everything actually works. And, you'll have a lot more appreciation for what those distro-suppliers
have to deal with
when they do what they do so well. The distros purposely insulate you from needing to know the gory details, but, to know those gory details is very informative. I think I learned more about Linux from
that, than from any other source of information.
("Use the Source, Luke!")