I have a three (blaze, white and coyote) but honestly rarely use them.
three primary places I use them are:
- I have a blaze orange one I use rifle hunting for visibility on my pack
- snow campin, they can be great on the move and also keep your pack fr9m loading up with snow when you set it down in powder
- when I know it is going to rain a good chunk of a trip. I will plus up my whole rain gear kit and use a pack cover as well.