You should never see more than 11 at a poker table.
Yes, obv. My point was that theoretically you could serve 22 off of one deck based entirely on total cards needed, therefore there is absolutely no need ever to have a double deck used for play.
Any more than that and it can start screwing with the odds to catch your outs.
How do you figure this? The odds of catching an out that you need is unchanged based on how many people are at the table. It is based on seen and unseen cards.
Examples (hole cards and flop exactly the same each time).
1. HU game. Flop comes out. You see your two cards and three flop cards. Five SEEN cards. The odds of you hitting an out you need is X.
2. Nine person table. Flop comes out. You see your two cards and three flop cards. Five SEEN cards. The odds of you hitting an out you need is X.
3. Twenty-two people sitting around one really big-ass table, being silly and all trying to play off of one deck. Flop comes out. You see your two cards and three flop cards. Five SEEN cards. The odds of you hitting an out you need is X.
In each case above, absurd or not, your odds of hitting your needed out on the turn or river is the same. It isn't based on how many cards remain in the dealer's hand, it is how many cards are seen and unseen (five and forty-seven, respectively).