Why do you lease your horse?

I have my own small farm with boarders. I want to add another horse to my herd whose main function will be as a companion to other horses and someone who tolerate being brushed and sat on my small children.

This is my first time ever shopping for a small horse/pony. I've always had sport horses. I always keep my horses until the very end. I can't even imagine selling a horse. Looking at all these ponies ending up in auction because their families outgrew or tired of them is breaking my heart. I'm thinking about getting 2 small horses and leasing one out so it can always come home between families.

Would love to learn about everyone's experiences.