With certain DLR packages, you are offered this "preferred seating" as a bonus. It is just special seating to shows like Aladdin, Muppets 3-D, Turtle Talk and It's Tough to be a Bug. With the preferred seating voucher at Aladdin, you have your own line and you get in ahead of time to pick out your seat. With the other shows, you have reserved rows which are blocked off for those with the vouchers.
I agree with DLR29 who just beat me to the punch, that it's not necessarily that great of a perk.