For years I would get a new camera and leave it on default settings for every button and dial. Then, as back-button focus became integral to how I shoot, revolutionizing the way I use my camera, I grew curious as to what else I might be able to improve. This sent me down a rabbit hole of creating custom functions, assigning new buttons, and reassigning old ones. In fact, I used to create so many that I'd forget much of what I'd done and go about doing a single button's work the long-winded, manual way.
Nevertheless, I now have lots of custom functions that I use regularly and it's important to my efficiency when shooting. The issue with many videos showing you how to "setup your camera" is that the photographer showing you is actually setting up their camera to their tastes. This video by Omar Gonzalez is a higher-level version of those videos, teaching you your options rather than being prescriptive. So, grab your Sony body and get customizing!