I am just starting out and have used the ATV remote app too - it does a pretty good job if all you want to do is pipe iTunes to AirPlay devices.
As soon as you want to stream other content (Spotify etc) you will need AirFoil. I also use it to pipe system sounds to my AirPlay devices for Announcing events etc which can be pretty fun. "Excuse me Marty, someone is approaching the front door". Not sure if I can still achieve that without AirFoil or not. Am still learning thanks to the fine folks on these forums.