There are three different reasons to have a "range holster."
1. You shoot IDPA or USPSA and want to be competitive. You can shoot with IWB, but you're handicapping yourself. This brings up another interesting issue... if you're handicapping yourself in a game, wouldn't you also be handicapping yourself in a defensive situation? Hmmmm... another topic perhaps.
2. You live in a state that doesn't allow legal CCW. You can't carry IWB or OWB outside the range so you may as well use what's comfortable.
3. You are taking your first defensive handgun class. This is not an insignificant one. If you have never taken one of these classes before, you're about to get a HUGE amount of information. You'll be doing things that you didn't consider and doing it a lot. Yes, you can use an IWB for this, but if you do, you're limiting yourself. You're going to spend more time adjusting the gear or fighting your shirt. You'll be concentrating more on the holster than you will your gunhandling skills. Take a class with a good OWB to get the basic skills and then take those skills home and practice them with your carry gear. The cadence is VERY similar but you'll learn more with an OWB and the more you learn, the more you can apply to your real life gear.