I usually run about 40 runs of IBT with the Xtreme Burn thing on, max RAM.
When/If it passes that I run Prime95 (version 27.X) custom with max RAM there aswell, for 12+ hours.
Will I ever run my CPU at 100% daily? Probably not, but I want to be sure that it can handle anything I throw at it, I might not be using it for very CPU intensive stuff at the moment, but when/if the time comes I don't want to crash and then have to figure out how to make it stable enough to pass that application, rather just have it like I said earlier, rock solid and able to pass everything I throw at it.
Others might not agree, but I don't care.
Stability > Speed.