This is a discussion on Why straddle? within the online poker forums, in the Learning Poker section; I'm curious what the advantage is of putting more chips into the pot without knowing what your cards are. Is this common practice in deeper
This would never take place in a tournament. It is a strictly cash game thing.
Straddles are often used to shorten the effective stacks, when everyone is really deep. It just makes the game play bigger. If the whole table agrees to straddle, the negative impact is shared with all the players. So, it's not horrible. If everyone isn't straddling, then it would be a losing play.
About the only time I consider a straddle is when you can "Mississippi Straddle" (often called a button straddle). This is where you post the straddle on the button and get to play in position preflop as well as the rest of the streets. This is fun in games where I am going to play my button nearly every hand anyway, so it doesn't cost me much. It really sucks for the blinds, because they have to act first pre-flop, which takes away their only positional advantage.