I am training for both. Every so often I find an accident off of the pad, but it is rare. What is happening more for me now is that my pups will miss the pad (have their booty hanging off) and pee or poop beside it. So, we are working on that...
But I like them to be trained for both in case I need to be gone an extended amount of time or for bad weather when they just don't want to go outside. It gives them a safe way to relieve themselves and if I miss a potty time and they have to go.. they can.
I think it is just important to keep the pads in the same spot