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 had two, and it was useful because I could just switch from either one. But one was a size big and one a little small, so it depended on my mood which one I used.
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.
It depends if each saddle has a different use. If not sell the saddle you dislike the most. I have a pony saddle and horse saddle. I find it very useful for my various rides.
Do you use it? Does it fit your horse?
If they're the same seat/tree size you probably don't need both, but it's always good to have a variety of saddles if you'll be riding different horses
No, keep it for emergencys