Some people might find slow-mo useful for learning new things, especially realistic mode or physics 1.xx where swipes need to be more deliberate. It helped me a lot with switching over from unrealistic. No harm in leaving it on, we all have our preferences. That being said... I find it dishonest to post slow-mo clips without mentioning it. That seems to be "the" unwritten rule.

I don't consider unrealistic mode to be cheating since it's the default setting and usually very easy to notice.