In New Zealand it doesn't seem to be so much of a common thing to haul your horses loose, so it makes me a little nervous
My boy has always been trucked until I got him, he didn't know what a straight load trailer was (most common thing in NZ) so he is very unbalanced standing straight in the float. It might seem strange I'm not sure, but I do prefer to haul him with the partition in and him tied up, just to get him used to it. I take him on random journeys to help him get used to it and he is getting much better.. Just recently I took him on a drive that took an hour and a half (mind you I was pulling over for other trucks and horse trailers as Mitch has to take corners veeeery slowly for now) through extremely windy roads both up and down hills, and by the time we got there he was almost asleep in the float, the journey home(next day) was half an hour faster as I didn't have to slow down to snail pace for the majority of the corners.
-Reason being that I have the partition in is because at 16.1hh and wearing a 6'6" cover, Mitch isn't small, and not many floats around here will accommodate that big of a horse should he want to move about and possibly turn to face backwards. I have seen him turn around in that float (when we were teaching him to reverse out of the float) and it was not pretty, he got stuck halfway around and I had to step in and actually forcefully pull him out, but this is a straight load 2-horse trailer remember.