Full fenders keep the dirt off me. They don't keep it off the bike; the only way to keep a bike clean, that I've found, is to hang it up in the garage and never ride it. But I've gotten to the point that all my bikes have fenders.

If you have 'full fenders' that don't keep the dirt off you, they're not full enough. A lot of 'modern' fenders are pretty skimpy, lengthwise, in comparison to the old ones.

For example, look how long the front fender is my old Norman (below). These are the original factory-installed fenders from 1950; the front one also had the leather flap, now long gone. Not that I commute on this bike, though. I have to commute on a folding bike.