If you're riding/taking multiple horses to a show it easier to have two saddles rather than constantly swapping. I use my own saddle and my trainers saddle whenever my two horses classes are really close together.
I own one dressage saddle and one jumping saddle for my horse. We have 3 horses and the other two horses have one dressage saddle each. We also have one older saddle that suits a lot of horses in our cellar just in case on saddle needs to go somewhere to change its size or something like that.
So I think to have 2 saddles for one horse is absolutely okay.