Buffering ...
You would expect the system to run well through Riviera station, one gondola in, one gondola out, one gondola in, one gondola out.
If a delay occurred, say, it took a long time to load a wheelchair guest, then not only would gondolas clump up behind but there would be a long section of empty cable departing Riviera. Now the clump has to be let out of the station with gondola spacing a little closer than normal.
If a clump were maintained at the front (exit) of Riviera, then in case of delay gondolas could still be exiting with normal spacing on the cable, at least for a short time, maybe one minute. It would then not be necessary to stop the whole system as often to minimize empty cable and minimize unusually close gondola spacing.
The disadvantage of any clump en route is that each and every gondola has to sit through it, advancing one car length, er, one gondola length, every ten seconds or so. A clump maintained so as to average six gondolas in size at the exit would add on average a minute to each and every guest's ride.
A clump at a terminal station (currently any station other than Riviera), if after the unload area and before the load area, would not arbitrarily add delay to each and every guest's ride.
Today I am guessing that the system would run more efficiently if wheelchairs and scooters entered the gondolas forward at Riviera (and backed out at the destination) while backed in at Epcot and Caribbean Beach so as to go out forward at Riviera if applicable.