Horses should not be stalled with riding equipment left on them, they can injure themselves if something were to get caught (the girth should be loosened and stirups pulled up while in a resting state for the horses comfort. This makes the saddle easy to slip out of position and spook the horse).
There is really no reason to keep a horse saddled when not being ridden, especially after being ridden.
It takes 5 minutes to saddle a horse and put the bridle on.
For all there power, horses are quite delicate and require some care in keeping them healthy and happy.