There might be an advantage now. I read a report somewhere (I think on Deb Will's site) that if you book Mears online, you print out a receipt/confirmation with a bar code.
When you arrive at the airport, there is a machine where you can scan that barcode and your tickets will print out automatically.
This will be a time savings over those that have to go to the counter to purchase tickets or exchange vouchers.
They aren't sending out the Disney $3 coupons anymore, so there is no advantage to not booking online.
It is essential to book online if you need a wheelchair accessible van, as there are only a few of them for all of Orlando, so you need to make sure they know you are coming.
Carol