[crockpot]

generally speaking, the gains from raising preflop - small +EV in value - are not worth the costs - knocking out lesser hands and poor draws that may call you all the way. also, by making the pot bigger, you are making it a smaller mistake for people to chase you postflop, which is an important concept in omaha when someone can virtually always draw to beat you.

edit: in tighter or shorthanded games, raising is important. however, you're not really raising because your hand is that much better than the opponents', but to outplay the opposition later on.