1. I am not a naturally organized person, but I like to give gifts. If I buy a gift in June for Christmas, I lose it and then you don't get it until next year.
2. We can keep spare gifts there in case we have a last-minute thing for which we need an appropriate hostess gift.
3. We keep all of the wrapping materials, cards, and gifts in the same room, so prepping is easy.
4. I don't forget where we keep the gifts. This was a problem at our old apartment, and we wound up with multiple gift locations.
I do even put gifts for my spouse on the gift shelf, but I usually wrap them first. He doesn't go through it unless somebody's birthday is coming up. It's worked really well for us - on Black Friday, I bought his mom's Christmas and birthday gifts, and just stuck them both on the shelf. It meant that we didn't forget that we had gotten her something, because we checked the shelf, and it means that we can be more efficient about shopping. We can also buy small things as stocking stuffers, etc. when we are on trips and just unpack them onto the shelf. It works really well, because then we aren't saying, "didn't we buy something for everybody when we were in Hawaii?"
My parents do the same thing - my mom used to keep a bin of stuffed animals for emergency baby showers, my dad has an emergency stash of gift knives. I really never knew that it was normal to bring people a bottle of wine until I hit my twenties. I really thought the appropriate hostess gift was a paring knife. We now have an emergency stash of wine as well, but that stays in our wine cellar (er, coat closet).
Do you have a gift shelf or another stashing place for keeping gifts?