Riding horses is like to play music: you need to know which are the notes on the keypad !! If you know the notes you can play and compose everything you desire.
The flat work on the riding horses meant to give the horse the seven notes of the keyboard, and you as rider can play with him !
If the horse has a good basic training you can do much more whit him.
You can have better result in your dressage, eventing and show jumping or simply have more fun and enjoyable riding.