It's definitely not AFKable in Draenor. Especially in Frostfire and Nagrand where there are a lot of hills. The bot will get stuck in a loop going up a hill, digging then going back down the hill, dig again. It only happens in a couple of areas, so as long as you don't leave it unattended for long periods of time and do these areas manually you'll be fine.
In old content is perfect.