Current delivery and immediacy seems to be the defining point. At least in my system anyway. I was plugging my amp directly into a high quality outlet to much better effect (another important thing to consider btw), until I got a good deal on a used Chang Lightspeed power bar and filter that touted “unlimited current”.
With that in place and everything plugged into it, literally no difference than plugging the amp straight into the wall in terms of dynamics and scale. But a slight improvement on background there from what I can tell.