Disabling it doesn't really work right. It doesn't let you still see history from when you joined; it just lets you see whatever bits of history your client has cached, which resets anytime you restart the client (on desktop) or anytime the client loses state due to memory pressure (on Android, no idea about iOS.) It doesn't really make much sense.

I guess the desktop behavior kind of matches IRC, but it's not what Discord users expect; the mobile behavior is just random, since you can't control when the client is "connected" or not.