I have configured custom Android kernel builds to enable more USB drivers, enable module support, and tweak various other things. For one tangible example of the result: I could plug in a USB Wi-Fi adapter and use it to simultaneously connect to another Wi-Fi network with the internal NIC while also sharing my own AP over USB. On an Android device of all things. I have also adjusted kernel builds for SBCs (like Pi clones) to get things working at all.

I have never seen any reason to configure a custom kernel for my own desktop/laptop systems. Default builds for the distros I've used have been fine for me; if I'm ever dissatisfied with anything it's the version number rather than the defconfig. The RHEL/Rocky kernel omits a few features I want (like btrfs) but I'd rather stick to other distros on personal systems than tweak a distro that isn't even meant for tweaking.