QUOTE(jchue73 @ May 29 2014, 12:27 AM)
You really believe it does not get back to the mitts, do you?

Some dirt you can see but most you cannot with the naked eye.
In order to achieve this optimally, you'd probably need to frequently change the water in the bucket.
The video test is a little flawed. It assumes all dirt are huge and heavy. The ones that causes swirls and marring are always the smaller lighter particles.
Anyway it's easy to just spew out Google searchers. The ironic thing is that in those searchers, there's pros but also cons about using grit guards. So there you go. It's not bullet proof solution. First hand experience and logic also tells that it's good to have if you choose to wash the way people usually wash their cars.
well, it's up to your believe on what works and what doesn't.
sifu krismas also pointed out you don't need to have grit guard. in fact, if you're OCD enough, feel free to try out that method scoutfai linked

in a perfect world you'd probably have industrial grade PW's and ready buckets of filtered water with/without grit guards and high pressure blowers fitted throughout the entire room so you never even have to dry and risk marring etc.
but hey, i don't live in a perfect world so that's that.