A little bit of both; it's a case-by-case situation. Shifting is all well and good to alter surroundings, how energy is manipulated, things like that. But the second you apply it to a sentient creature you have problems. Minds and souls are such delicate things, after all.

In the case of interference...well, that's a little harder to explain. Let's just say that whatever brings you here isn't as structured a phenomenon as we'd like it to be.