Ok, so you're at a concert and they are selling drinks inside. But, they won't let you in with yours because then they won't make that money off of you. Plus, sometimes they don't have what you want inside.
Problem solved NOW! You can take your drink with you and if they pat you down, say, "Hey, that's my beer gut! Go laugh at something else!"
I said it was the best invention known to man. Now, was I wrong?