This rule is highly controversial, and there are fervent supporters on both the pro-elbow rule and anti-elbow rule sides of the debate.
Arguments in favor of an elbow rule include:
1) It eliminates the advantage that taller/longer-armed players might gain by leaning or extending their arms over the table.
2) It makes the game more challenging and slows the pace of games.
Arguments against an elbow rule include:
1) Elbow rule is almost impossible to enforce.
2) Watching your elbow position and arguing about it wastes time and detracts from the game.
3) Faster games are better when you're trying to finish a tournament or people are waiting to play on the table.
The World Series of Beer Pong (WSOBP) in Las Vegas every year does not require use of the elbow rule. As a result, leaning over the table is the norm and teams that insist on following the elbow rule are at a disadvantage. No elbow rule-following team has ever made it anywhere close to the WSOBP finals in the four years the event has existed.
Frat boy #2: "Let me see..." (watches video) "Yeah those guys are a joke! If we went to the WSOBP we could win that shit easily! Let's post a comment this YouTube video."
Frat boy #1 posts comment: "Watch your fuckin elbows! You guys suck and we could beat you any day. We are Lambda house champs and we could make every shot if we leaned over the fuckin table. Leaning is gay!"
(Smashing Time sees comment and they arrange a cash game for $500 a team)
Frat boy #1: "Ok we'll let you guys lean as much as you want. We're not gay so we're going to keep our elbows behind the table."
Smashing Time: "All right, whatever."
(Smashing Time wins by 8 cups)
Frat boy #2: "Well it's pretty fuckin' easy if you lean way over like that. We're gonna play again for another $500 and lean this time. You guys are going down."
Smashing Time: "Ok, I'm sure you guys are gonna kill us this time."
(Smashing Time wins by 7 cups)
Frat boy #1: "All right. Let's play again for another $500 except this time we all have to keep our elbows behind the table."
Smashing Time: "Let's go."
(Smashing Time wins by 7 cups again)
Frat boy #2: "You guys are fuckin' cheaters, leaning and shit. We're out."
Smashing Time: "All right. Good games. Thanks for the $1500."
Frat boy #1: "Whatever man, let's go to next year's WSOBP and show those leaning bitches what's up."
(Frat boys go to WSOBP V and finish in 378th place with a 2-10 record, including losing to an all-girls team who is just there to promote a hangover-curing drink)
Frat boy #2: "Dude, who gives a shit. At least we're not leaning bitches. We showed them."