The foot pedal with auto throttle on DOES BOTH. The more you push the faster the engine speed and the faster the hydro speed. Otherwise with auto turned off the foot pedal works like the cruise handle.
I have a L3240HST, FEL with 6' RFM. Also box blade, landscape rake, Fergueson reseeder, forks (which I used yesterday to unload a refrigerator off my truck) and a fertilizer spreader. I now have 17hours on it. I previously owned a B7800 with these attachments. It has been a learning curve with the auto HST, using cruise, auto throttle and auto hst. I've discovered that there is not one best for all. The auto throttle is great for FEL work but I disengage it when moving the load to the dump site. Mowing I set it to auto hst and set rpms to 2700 and then drop it down to turtle by hand when it starts slowing at the crest of my hill. I usually operate in low because of my hillside and rougher terrain. Like using cruise only when driving across from one side of property to the other side with rpms around 2000. Wasn't to satisfied with my trade until I tried the different combos for the different jobs. Guess I learn better by trying than reading. Good thing is HST shouldn't tear up while your trying what works best for you for each job. Again, I have hillside with ditches and rougher yard. I use most of my attachments from time to time. Get out there and try the different combos and see by experience which works best for you.