The volcano is extremely effecient.
Here are some numbers:
Joints/Blunts: 10-20% THC "consumption"
Pieces/Bongs: 30-40% THC "consumption"
Volcano: 95% THC "consumption"
I forget where I read these percentages, but I wouldn't doubt they are accurate.

Basically, after having a volcano for a solid 5 months, I've found that I save a ton of weed, its like I almost double my weed when I only use the volcano.

As for temperature, I've read numerous times, and from my own experience, 10 gets maximum THC extraction... Anyways, just think about it. Makes sense, doesn't it? And putting it at 10 means more vapors/bag, getting you higher, faster. Bag filling can get a little tedious.