Just like in hold'em, position is an important element in Omaha. Many consider it to be even more important when taking into account all the possible combinations a player can make with an Omaha hand. When sitting in position, you can follow the actions of your opponents and make your decisions based on the information you received. When out of position, it is much harder to make the correct decisions because you are dealing with incomplete information more often.
Another benefit of being in position is that you have a better chance of controlling the size of the pot, which is often based on the strength of your hand and your overall goal in the pot. Being out of position to one opponent or more gives them the ability to control the pot size and also capitalize on the added information of knowing your actions first.