Just to be clear - on the way I do it - the engine is off when I "clutch" down the ramp. Just using the rear tire and 1st gear to control my descent.
My purpose of firmly wrapping my hand around the throttle is to avoid the temptation to grab the front brake - it will do nothing but add excitement.
As long as were talking unloading.............
Loading
The ramp can get awfully steep when you first start using it, especially at the point where the back edge of the ramp is about in the middle of the bike. Your feet are about 17 feet from the ground. Well not really, but sure feels like it.
When I load the bike I make sure the bike is square to the garage, I do not want to make any steering corrections. And once I start, I pretty much commit to getting the bike in the trailer.
Stopping midway can be bad.
Wet ramp can be equally bad. I do have a winch in the front of the trailer which I would use if I had to load in the rain, rather then take a chance.
Loading and unloading I will try and use the natural terrain if possible. One example, in my driveway, If I go to the end, I have a flat load from ramp to garage. But I can't get the bike out there, once off the ramp it is all uphill.
I will occasionally raise the front of the trailer as high as possible to make the transition from ramp to garage less "dynamic"