Well, I got no research to back this up, but holding it longer doesn't get ya' higher.

If anything, it deprives your brain from oxygen so you might get a light-headed/placebo effect and think you're more high.

More potent weed shouldn't do more damage to your lungs, its an increase in THC, not tar.

Don't worry too much about lung damage, weed won't give you lung cancer, its been proven there is no connection between weed and lung cancer. As for other stuff related to lungs, I don't know. I'm not too worried though, so many people smoke so much more than me and don't seem to have terrible lungs.