The biggest thing IPIU does for you is provide you with an easy way to gain the experience most states require prior to issuing a license. A commodity that can be extremely difficult to come by on your own.
Most independent private investigators don't have the time to train someone, and agencies usually want a license or experience coming in. It can be tough getting your foot in the door.
Personally, I think this is the most valuable service the IPIU provides it's members...taking the hardship and frustration out of getting the experience and getting certified.