I think I started doing this when I was in high school. It's presonal preference but I think I picked it up from skeet shooting so much. But, I for one, hate seeing 'litter' in places I hunt. I mean, there's been places where garbage...washers, driers, chairs, cans, etc. (basically old dumping sites) and I can't stand this and I think that's what mostly caused me to do this. My dad doesn't usually pick his empties up but I just feel better for doing so.