As of now my horse has shoes on year round because the ground is a little tough and when wet can be really bad, and in the summer when the ground is pretty decent I ride a lot more. Also my horse has feet that tend to grow a little weird and shoes help keep them in line.
I used to at an old place I had her where the ground was perfect for horses like everywhere even on the trails, keep shoes on her only in the summer when she was being ridden a lot more but winter I had them off. Even with them off she did fine on trail rides and arena work, but with it being winter it wasnt as heavy and as often. I probably even could have left them off in the summer but I like to be safe and with the way her hooves grow it did help.
But that's just my opinion, there is so much to consider!
My friend had an old mare and she would have just her front feet shod as they seemed to be a little weaker and that worked really well for her.