With me, reliability and Stability of the OS. I never have to mess with it. I do run some small maintenance on it every couple of months but that is it. When I need to get something done, my Computer and OS are ready and waiting to assist me. I don't have to run virus scans and malware removal first. I run 10-15 things at the same time 24 hours a day and it never lets me down.

That alone saves me so much time and makes the computer a joy to use.