Faster drink service, feeling cool, etc.

It's a bit of a dick move, and takes away from more than just other customers. I'm the house musician for two local breweries and contract to three others in my area, and between sets it's best to be able to place an order really quickly. Large groups ordering 6 or 7 drinks at a time make that impossible and it's pretty inconsiderate to the bar tender.

That's my personal, rather selfish, issue with it but all around I'm not a fan.