When is it wrong to not C bet heads up in a pot?

I've been watching lots of videos about C betting and the pros give a wide range of responses on when and how to use it. Take Gavin smith for an example. He C bets 100% of the time heads up. This goes with Danny negreanu green stein and other pros. However gus says u shud c bet about 80% of the time so that it allows you to control the pot size, slow play or whatever. I'm with Gavin being the most profitable strategy is c betting 100% (obv if I put my opponent on a range that will hit the flop more often than not, or if I think he has a pocket pair I wud check unless qualified (I hate that word used in poker btw) haha.

So what do you think? Please give me advise I really need it because I think this is/ could be my biggest leak because it ranges from being very profitable to throwing money away.

If you have a hand with showdown value and you know your opponent is capable of bluffing when you check to him. By doing this you allow your opponent to give you value you would never have gotten if you had cbet and he folded.
Remember only to do this if you have a solid read, theres nothing worse than facing a river bet oop with a bluff catcher and not knowing forsure that your opponent is capable of triple barreling with air.

When you flop something huge like nut full house or quads you need to let you opponet catch something in orther to extract some value, since you hit the flop so hard is very likelly it missed him.

If you flop a full house you need to bet.

It is probably never wrong to C-bet, but there are times when you will lose value (-EV) by doing so. Flopping a huge hand for instance, and stringing a LAG bluff along till you strike on the river.......These are the more fun hands.........

Fit this into the "changing gears" category.

Well if you always barrel then c/f turn then its a major leak. Heads up though, its a lot more important to vary your play since your opponent is (and should) be watching you like a hawk. We assuming this is only heads up?

If you have a hand like AK and flop comes AAK, I believe you can extract more value by not c-beting, you hit the flop so hard that your opponent probably has none of it, why not give him the chance to catch something or bluff at it.

Yes I c-bet almost 100% time unless I flop a monster....like AK with AAK board....