Not all theme park shuttles are equal. Many hotels have limited shuttle service. They have one or two trips in the morning and one or two trips back in the evening. That's fine if you are planning on spending all your waking hours at the park. However, it can be a major hassle if you miss the bus.

Also, be sure to check the shuttle destination. It's less of an issue with Universal, as their two parks are adjacent to each other. It's a bigger problem with Disney. Many of the hotel/motel shuttles only go to one of the four Disney parks. Once you get to that park, you'll have to use Disney transportation to get to the other three parks. That ends up being a major pain.