Should default device management be removed from VTK-m?

In the discussion on !679 (closed), @kmorel brought up whether or not we should have default devices in VTK-m.

Changing the default device seems a bit clunky to me as it introduces header dependencies, and a default device mechanism would be trivial to implement from an application.

Does the default device system in VTK-m serve a valuable function in the current design, or does it just add complexity?