I would find it very handy if there was a load up command, as atm you cannot efficiently tell a large number of transporting vehicles to load up a large number of other units. Using ferry will indeed automatically load units in a efficient manner in their transports, but they will always be transported somewhere immediately after having been loaded up. Deleting the destination waypoint for the ferry does not help btw. The destination point will then become the load up point, which is really pretty silly if you ask me...
So what I would think would be great, is a simple load up command that exists in addition to the ferry command. You select a group of transports and place a load up beacon for them somewhere on the map, just like you do with the ferry beacon. Then you assign the units to be transported to the loud up beacon, the transports will swarm out and load up their respective units and then form around the load up beacon and land there.
Maybe other people would like to see something like that too... would that be possible to implement?