It's very common for lower-stakes players with a pair such as pocket aces to use a double raise to keep their opponents in the pot. But why would you want to keep your opponent in the pot with only a pair, especially in No-Limit Hold'em?
A double raise is a huge mistake in No-Limit Hold'em because you're giving the other players great implied odds to hit their hands. For example, say a player is sitting with $600 and raises the big bet to $12 with pocket aces. Based on the math, you should call with almost any two cards because if you hit your hand you'll almost always double-up.
In this example we'll assume that you suspect she has aces, but aren't quite sure, and you have pocket queens. You move on to call her pre-flop and flop a queen. She bets hard and you take her whole stack. While she's sitting there whining to herself, you smirk at her, having known exactly what she had the whole time.
The next time you play online poker or make a trip to the casino, keep this small tell in the back of your head. You'll be surprised how many players love doing this - and it's the kiss of death for new players.
Not only is this tactic good pre-flop, but it's a great post-flop tell as well. When there's a straight draw out, and it looks as if an opponent has hit it on the turn, many people will raise your bet double. This raise is almost begging you for some type of call, but you can immediately fold, knowing that you were beat when she hit her draw.
It's surprising how often I've seen this situation happen when playing online. I started a log of every time a player had pocket aces or kings when they raised double pre-flop and I found that, out of 20 hands taken to showdown, 17 of the people who did double raises had pocket aces or kings.
It's a very logical approach to think that raising double would net some profit, but the problem is it's not a high enough bet to weed out other players. The more players in on a pot, the less likely your aces or kings will hold up to win it. If you want to take down a pot, you have to get out of the habit of raising double and vary your bet sizes to keep people in when you want them to play and scare them away when you don't.