I notice KDE's resource utilization more or less constantly. With KDE's bling turned all the way down, Kwin constantly uses 5-10% CPU when I am literally doing nothing (with my hands off the mouse/keyboard). This causes my laptop fans to noticeably spin up and makes them a lot more prone to spinning up more forcefully while doing a small task. With XFCE, my fan never audibly spins up unless I'm actively doing something. Even if I just do something small/quick, my fans don't spin up most of the time.

edit: typos