I also take it out (hauling distances 2-5 hrs.). My horse like to have
some space. she prefers to stand a little diagonal, leaning her backside
on the rear pole. In this manner she stands very calm for hours. I
cannot say if she's happy or not, but I never hear any noise while
She also prefers to turn around and leaving the trailer forward. So I
decided to leave the divider away and practiced this for years with no
negative effect. Even if I haul two of my horses I leave it out (of
course there is still enough space to move and they wear booties).
There are some people who would disagree but I wouldn't take someone
earnest who isn't hauling really long distances.
If someone ask me loadby another horse I say "sorry I have no divider, I
can't be sure if they don't bite or kick one another" ;-)