Humour - use it or not?

I've been pondering over a challenge from one of my students all week which is humour, do you use it in presentations or not. My stance is if you are going to use it, use it in moderation, make fun of yourself and no one else, and dont tell jokes, leave that to comedians. However, my dilemma lies in the fact that some people are jovial and funny all of the time, so their style is to be funny which contravenes my rule. My fallback position is if you are naturally funny be yourself, but only, and ONLY if you know the audience, if the audience is new and unknown, they are more likely to respond positively if you inject that humour, slowly and casually, let them get used to the funny you.