Checking out the field before you start a match is very important for both you and your paintball team.  If you know the field well, you will have a huge advantage over the opposing team.  If you are a back player, it is very important you check out the field so you know your lanes to shoot.  You need to know the paintball field to have the right angles on your opponents, and to know where your opponents will be able to see you; not to mention knowing where the best cover is.  Sometimes after looking at the field, you may want to change your game strategy at the last minute; we've done this and it's helped us win the match.  Whenever you go to a tournament, try your best to check out the field before your match.  You have to know what to do and where you're going during the match.  Know your surroundings while playing in paintball matches; any advantage you have over your opponent is a good one. 
Mike Morton, Team Trinity