I never used it myself, but now I think about it I realise it could be quite useful for one-handed multitask-playing.
The more important question is, though: WHY ON EARTH HAVE WE ONLY GOT ONE HOTKEY?! There's 4 face buttons, two shoulders and the Select/Start buttons. Clearly A and B are in use, but why do we need X to open the menu? It was far better in HG/SS as a purely touch-screen menu. And why can we not use Y, L, R AND Select to register 4 items instead of one? It's annoyed me since I can remember that you can only register one item. Imagine if we could have the Bicycle, the Map, the Super Rod AND the Vs-Seeker all just a single button press away...
Not that this is the only UI inadequacy in Pokemon games. For example, why can't we choose to Fly to a city straight from the Map screen? Instead we have to press B, go to our Pokemon list, select our Flyer, then click Fly, then find the city all over again... Urghh.
Sorry for getting off-topic. I did answer the question at the top though...