Platooning quarterbacks

Platooning quarterbacks is when a football team uses two (or more) quarterbacks to run their offense, rather than the traditional one in American football. This tactic becomes less common the higher the level of football (high school teams are more likely to do it than National Football League teams for example). Quarterbacks may be switched in and out of the game every play, every drive, every quarter, or depending on certain situations. If quarterbacks are switched game to game that is not platooning, that is a "quarterback controversy" or a simple benching.

Advantages
Using two different quarterbacks allows an offense to use players with different skill sets. One common reason teams platoon quarterbacks is because one player is a good passer and the other a good runner (see for example Stanley Jackson and Joe Germaine of the 1997 Ohio State Buckeyes). Thus defenses have to prepare for two types of quarterback, not just one. It also allows offenses to run a greater variety of plays.

Disadvantages
Arguably the most common reason QBs are platooned is because neither are very good. If you have a great quarterback, it does not make sense to remove him from the field on a regular basis. There is an old football saying "if you have two starting quarterbacks, you don't have one." Changing quarterbacks can disrupt the rhythm of an offense (and/or of the quarterbacks). It also makes it hard for a quarterback to establish himself as a leader if he is not always on the field. Also having a "running quarterback" and a "passing quarterback" can make it easier for a defense to predict what an offense will do on a given play depending on which quarterback is on the field. Rarely do team platoon quarterbacks as part of an active strategy, usually it is to make the best of a bad situation. Platooning running backs on the other hand is often seen as desirable, especially in the NFL, as a way to keep them both fresh and healthy.

"Smelley Garcia"
Southeastern Conference college football fans use the regional term "Smelley Garcia" to describe an unsuccessful use of platooning quarterbacks when both have similar skill sets. The name is derived from University of South Carolina quarterbacks Chris Smelley and Stephen Garcia who were platooned by the Gamecocks despite largely being the same player. It is not intended to be complimentary. In general fans do not want their teams to be platooning quarterbacks.

Non-platooning
Platooning quarterbacks is not the same a playing an inexperienced quarterback in certain situations to prepare him to be a starter once the current starter is no longer with the team. A team platooning quarterbacks is doing it because it wants to have both quarterbacks playing because they think it gives them the best chance to win the game. There can be cases where both apply (the Florida Gators use of Tim Tebow in 2006 for example).

Also using a quarterback only for one type of play (QB sneaks or Hail Marys for example) is not a traditional platooning. Both quarterbacks have to be running the majority of a teams offense.