The BG-E11 expands the Canon 5D Mark III makes sense to explore the possibilities, also in portrait relaxed to take pictures and to use two batteries (LP-E6) at the same time, respectively an approximately double working time without battery change. Here no operating convenience is lost because the battery grip is equipped with all the necessary controls in portrait mode.
Personally, I like to take pictures with a relaxed hand position and therefore prefer a battery grip with my cameras. In addition, the battery grip is more stability when holding the camera.
Only one display at the battery grip would be a nice-to-have.