For example, I'm using Debian, and I think we could learn a thing or two from Mint about how to make it "friendlier" for new users. I often see Mint recommended to new users, but rarely Debian, which has a goal to be "the universal operating system".
I also think we could learn website design from.. looks at notes ..everyone else.
Gentoo - patience.
But seriously. With the USE flags, compiler options, you can understand software more from a developer's point of view.
You can try to optimize software for your hardware.
Fully explore the configure options. With a binary package you have no control.