Another few reasons, atleast where I live , we keep fronts on in the summer once the flys come out because they constantly are stomping their feet and the shoes help them from bruising their soles. :(
And alot of people don't put back shoes on because if a horse kicks and he has shoes on in the back and connects with another horse it is alot worse. So alot of boarding places won't allow back shoes unless medically necessary.
In winter some people who keep there horses outside alot will have front shoes on with little spikes underneath to help the horse break through ice on the ground so they don't slip when they are running through the pasture.But that is up here in Minnesota where we get rain, then snow and that turns the wet ground below the snow into ice which can be very dangerous.
These are just a few reasons, hope it helped.