Sleeving is nice for aesthetics if you enjoy the way they look. Not sure there's really any other argument for them such as durability, the wires aren't in motion or being abraded once they're installed. They just sit there stationary and provide power. I suppose if you were constantly moving them around, rubbing them through holes in the case or something but how often does someone fiddle with the wiring? Outside of exchanging components or something and that's minimal, it's not a daily activity.