For a more complete explanation and discussion of this issue, go to Submitting Jury Instructions in a Bench Trial . In the meantime, today's opinion in State v. Massey is a good reminder why you should get the judge on the record adopting or rejecting jury instructions, even in a bench trial. Though there was enough evidence to survive MJOA, the judge's erroneous adoption of the Miles instruction in a bench trial resulted in the conviction being reversed.
As I have mentioned before, special jury instructions -- if they are accurate -- that the judge declines to give or follow (whether jury or bench trial) puts the defendant in a much more defense-favorable posture on appeal than a denied MJOA. When should you ask for a special jury instruction? Every time, but especially when guilt or innocence depends on an interpretation of a particular word or phrase. See the discussion here.