You'll get lots of candid photopass pictures of your child on stage and fighting the bad guys. It will include group shots that your child us in, as well as lots of just your child and the trainer and Vader when he/she is brought forward to fight. If there's a rainout, it is substituted with a meet and greet, where I'm guessing you might get posed photos taken.
My big tip: after the show, when the photographer gives you the photopass card with your code on it, take that card to a photopass shop (near the park entrances or at downtown disney) and have them help you upload the pictures to your account. You *can* simply enter the card's code on your Memory Maker page yourself, but this will put ALL the pictures including dozens and dozens of pictures of the other participants. At the store, the people can help you quickly selećt just your own child's pictures for upload (an option you don't have when you do it yourself). The photopass/memory maker site is slow and its a real pain to have that many extra pictures clogging up your page.