For the pedal input on the eDrummin, exact same use cases as MIDI Expression. Could also be a 'gateway drug' to people purchasing a MIDI Expression to be able to take advantage of the awesome features with more than one pedal.
For the pad inputs, stuff like
a specific action for a specific velocity range, using a certain strike (eg cowbell rim) in the same way as a pedal to switch between instrument sets, again pretty much the same set of use cases, just triggered with drumsticks instead of feet.
Personally I'm interested in playing pieces like this while Mobile with an Android, so trying to get the largest number of notes out of the smallest number of pads:

drumKAT improv, February 2015
Just a little fun in the basement.—drumKAT Turbo with DW EP-1 pedals—Logic Pro for piano sound—Digital Performer for audio and video synch—MacBook Pro —iPad ...