After my little ride earlier today, I was out with Chloe again, and she seemed to express a desire for me to climb aboard. With which wish I dutifully complied.
After a few moments' reflection, she set off through a gate which I'd left open to the other pasture so that she could have access to water while out on the lawn. She stopped for a drink, turned to face the other side of the field, and thought some more.
I said, "Chloe, do whatever you want, as long as it doesn't involve any rapid changes of direction or fast speeds."
She headed down toward the creek. The horses always cross the creek (whether dry or muddy) at high speed, so when Chloe stopped at the edge of the mire to evaluate the situation, I slid off.
She immediately became very imperious and demanded that I get back on. How did she express this? She looked exasperated, and shoved me with her head. So I remounted.
After a few more minutes, during which time she listened to me explaining the extreme precariousness of my situation, she set off across the muddy creek. She speeded up a little, but not enough to make me lose my balance.
Up the hill on the other side. Where does Chloe want to go now? Aha. The shelter. So in we went, and I got off. I don't think she was frightfully pleased about me getting off, but it was ok, because I scratched her a lot, and she dozed.
After a while, I think we both were thinking it might be time to return. We weren't sure (at least I wasn't) if I should ride or not. As I seemed to be going in the direction of her choice, Chloe decided that she could just walk beside me.
At the creek, we both stopped and looked. Chloe came up right beside me to assess. I found two dry hummocks to place my feet on, and made it across semi-dry. Chloe followed.
She was ready to go back into the other pasture. After I let her in, she waited for me to come in with her. The other horses were out of sight, so I walked with her until she could see them, and then she was happy to set off towards them without me.
So - the ability to make someone get on your back gives you the ability to command the services of a built-in buddy, who will accompany you wherever you go when you want to set off by yourself away from the other horses.