It probably isn't noticeable on newer computers, but on old (really old) computers it definitely is noticeable. I've never understood how updates are improving the performance. Sure, they can fix security holes and patch up software problems, but they always slow my pc down. The already limited space I have on my C drive would get even smaller.
And I have a limited number of applications on my pc (with zero running in the background unless I want to). It's not their fault.
I can't afford the newest i5 cpu and the 970 gpu, which can handle the updates without slowing down.
So I'm going to disable the updates every time. I don't even update my browser, since the newer versions end up taking most of my ram and lag.