During the day you won't be sharing as each AS fills up their own buses to/from the Parks.
Later in the evening, and especially at Park and DTD closings, all of the *** share so that the buses can be filled. You do then stop at each resort for drop-offs. We usually close down the parks at night, and stay at the Movies, so we're the last ones off (Music and Sports are dropped off first). But it's no big deal at that time of night.
Back in November it was the other way around, buses were generally shared midday and separate during morning rush / closing rush. At Magic Kingdom and Epcot, at least, the signs at the park bus stations are changed so three boarding areas are used for All Star people to line up during park closing, just one boarding area is used during less busy hours.
In the morning I have from time to time observed "separate" buses if not full, swinging into one of the other All Star resorts to pick up and fill up.
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