Here is the thing, waste is a relative term. Some people mean waste as in, to have a good joint you have to have at least a gram, preferably 1.5-2 grams. To have a 4 hits from the bong, only requires say .5-.75. See 1 joint gets more than one person high, so you have to take that into account. The norml studies are just measuring which is the least wasteful in terms of how much thc is lost from one hit. So the thing is neither are a wasteful use of weed. They are both just different in there own ways. Now what your friend was saying is that he wants to conserve weed, and bongs use up a lot of weed at one time, and it is harder to control the hit going into your lungs. The bubbler on the other hand makes it very easy to control how fast and how much of the weed burns, you can still pack a full bowl but corner it, easy put it out, take hits when you want. I know you can do the exact same for a bong, but the thing is you are forced to take bigger hits and you may not even need the entire first hit to get high. My entire point is that waste weed is not an absolute term. It very a ton for different people. I like joints a lot(though not good at rolling them yet they are my favorite kind. So I can say I think all other forms of smoking are wasting weed but that is just not true.) I do think hat using a bowl/mini bubbler or the best way to make your stash last longer and get more people high though.