Ok, so DRL may help an oncoming vehicle see you, or for a pedestrian to see that you are coming. But they wont do anything for the car that's speeding behind you in the rain.

Ok, you've made me realize that I'm using mine in a different way than most. I don't use my DRLs, I use the feature of my car that lets me leave my lights on all the time, while shutting them off when I turn off the ignition. I leave my light switch switched to ON all the time. This means my taillights are on all the time, too.