Map picking is an important part of every esport I have watched that has different map options, and Guns of Icarus is no different. Every single player I have played with has their map preferences, maps they like more, and maps they are better at. A map pick/ban adds another level of skill to a competitive game, and at the same time gives players more control of the match, removing a large amount of luck.
Teams have the opportunity to pick maps that benefit their own playing style, while banning maps that benefit their opponents, or they themselves are not very comfortable with. With the current randomizer system, maps could be chosen that give one team a distinct advantage over the other.
A team that knows how to use the picking and banning well will have an advantage over their opponents, using a different level of their game knowledge to gain an advantage.
Though picking and banning is possible for any variety of set sizes, it would work best in tournaments with sets of multiple matches. Though best-of-one matches like in a standard SCS could take advantage from a pick/ban phase, the tournaments that work the best will be those sets of 3 or more matches, such as the Big Brass Revival.
A problem we run into with the picking and banning is the fact that the current amount of 2v2 deathmatch maps is an even number ( 8 ) - meaning that if each team is given an equal amount of picks and bans, there will be an even amount of maps remaining. The possible solutions to this would be to either give one team an extra ban compared to the other team, or to have a randomizer choose between the final two maps.
What I do not understand at all, however, is the need to classify the maps on a scale of openness to closedness. To me, teams should be able to pick from the entire list of maps, without any restrictions. It should be up to the teams to choose which maps are played, not from a list restricting anything. This does leave the problem of an even-numbered map pool, but that is something we will have to deal with until then. (Maybe Santa Muse could adapt Battle for the Ball to Graveyeard DM, or one of the alliance maps?)