Drums,
I am unqualified to answer your question in any kind of depth. I'm only giving my little stab at an answer so someone smarter will notice an opportunity to give you a better one. Probably there are loads of people on here who could wax philosophic on the topic with great relish
Basically, I think how the vapor & flavor behave when different amounts of power/heat are applied depends at least in part on the type of set-up you have as well as the composition of the juice. I suspect there are a lot of variables ... more than I can think of and more than you probably care to know.
Disclaimers aside, in my experience, higher wattage gives more intense flavor up to a certain point, after which the juice burns and tastes like total crap. You definitely go through more juice when you apply more power, 'cause you're turning the juice into vapor faster. I think airflow is a factor too. More airflow tends to make more vapor AND give better flavor, again up to a certain point, after which you get less flavor. The incoming air keeps the juice burning at an acceptably cool temperature (i.e., turning into vapor and not burning) for longer, hence allowing more vapor to develop.
If you accidentally leave your finger on the fire button of your mod, even at quite low power, you will get a vividly unpleasant example of what one example of "more power" does--in this case, over time but without the cooling effect of airflow.
I think this is one of those things you will just get a feel for as you vape. People usually say to start low and work your way up, and that has worked for me as a general rule. Personally, I haven't felt the need to go above about 10 watts--and the one time I tried it (20 watts on a magma dripper, on which I'd built my very first, sadly deformed--yet somehow functional in a limited sense--coil), the result was horrific. That doesn't mean anything except that i am a beginner.
I'm sure there must be tons of good reasons to vape above 10 watts--reasons that don't have solely to do with my-mod-is-bigger-than-yours type concerns. Right?
edit: if you got an iStick, I suggest reading about the oft-noted (and complained about) vagaries of its power output. There is a way to talk about it that involves electrical acronyms--something having to do with something-mean-power vs. some other kind of power. One way to put it, tho, is that it runs a little "hot"--hotter than another device might at the same setting.
