Curious to know the coolest things you achieved by configuring your kernel. I know kernel config can be boring, but I'm hoping someone will have an impressive answer.
For me I have a very lightweight kernel that runs wayland on nvidia without any issues to date.
Years ago (2006-ish), I ran Gentoo on a 300mhz ultra low power system I used for an irc & web server. I gained LOTS of speed and lowered power draw even further while also enabling the hardware acceleration the board had for ssl encryption and video encoding. The whole thing would pull <5 watts and be super stable. It was well worth it.
But now days a Pi zero would trounce it in both low power draw and speed with stock kernels and I don’t really care enough to try to squeeze more out.