You end up buying things you might not have purchased if you were alone. Sometimes it's bad news bears (aka you head home loaded with shopping bags) and sometimes it's a pleasant surprise. Take this necklace for example:
I was with Beth and LaLa at the Grove last month and was monkeying around at the register while LaLa ordered her bridesmaid dress and scooped it out of the sale bin. The ladies persuaded me to buy it and it was a very good decision. I heart it. Purchase here while they last.