Bad experience here.
Ex-spousal had a young horse wanting to load. He decided to "practice loading" instead of just hooking up and hauling.
He wouldn't listen, so got himself and horse in trailer, all the way to front, and horse was fine but the weight shifted the trailer off the block, and it dropped. Not cute.
So, I am a firm believer in no loading with being hooked.
And don't like to tie to one either, but at barn I work at, we do do it, but I am always leery of it.
Horses make me a better person.