I actually don`t know much on this topic, so I`ll be interested to hear what people have to say. I ride hunter. Personally, I always encourage to horse I`m riding to bend using inside rein + inside leg. It gives them something to lean into and bend around as they move around the corners. With stiffer and greener horses, their turns become sloppy and unsteerable if I don`t bend them, because they can`t easily make it around the corner without the support of my inside leg. However, after I initially begin the turn uside inside aids, I slide my outside leg back an inch and apply pressure to complete the turn.
I`ve never been told anything in specific about corners, I just basically played around and figured out what works bests to get the results I want. However, I`m sure that other people think differently, and I`m very interested to hear what people have to say on this post. :)