I'm still trying to understand the game engine and to be honest the offside trap is a load of rubbish. I tested it last season several times against noob teams with no offside trap and offside trap and I tended to concede more goals with offside trap... Against noob teams as well!
Whole pressing still needs testing, however I score more goals with an attacking mentality and own half pressing. It also reduces the chances of you being hit on the counter attacks, especially if you have red arrows on your defenders.