While not a huge thing for some people, we really like to get at least one nice souvenir while in the parks, especially when we go to Epcot. It's really convenient to be able to have it sent to the hotel instead of having to figure out where to put it/store it or lug it around all day. Also, when determining between onsite and offsite, we try to factor in mileage from the parks, probable traffic in the mornings to get into Disney World (it's usually crazy lines at the turnstiles, and you bypass this with the onsite buses), time walking from the parking lots to the gates, and gas to drive back and forth to offsite lodgings.