As a multiboxer you will almost exclusivly do better at defense than offence, atleast if you are a decent pvp'r. If you are going to cap bunkers(or towers if you are alliance) you have to defend them for 4 minutes and you cant help your raid out in any other way during that time. If you are defending you can recap 2-3 towers(or bunkers) in that time, since you most of the time will just steamroll those defending it.

The only time I decide to attack is if a lot of my team matess are defending, and allys are doing the same.