Not as useless as you would think... Think of it like this... Your shooting a couple outdoors, open sun, you set your exposure... all of a sudden, a cloud comes overhead... you need to instinctively know to compensate... is it 1 stop or 2? Is it a thick light killing cloud or a thin softbox style cloud... Then you go into an open shade... what affect does that have not only on exposure but color?
awinphoto - do you also change WB on the fly or fix it in PP?