The majority of players keep their hearthfires indoors, and that same majority rides horses regularly.
Horses are not able to go up cellars, or up/down stairs. They also have a lot of trouble with doors.
In my case (a greathall), every time I port to my hearthfire I need to leash my horse, go down the steps (then hope it doesn't bodyblock me), head outside, unleash the horse (it usually runs away somewhere in the plot at this point), and then get back on to it.
Do this a few hundred times and you begin to hate horses.
Could something be done to make it possible for us to go up down stairs/cellars while on horseback?