Think about this. When I had first started smoking cigarettes if I "double hit" my cig I'd get a nice headrush, more intense than just one long drag. So with bud would it work the same way where I'm getting a quicker rush? This kinda goes back to the theory of how your lungs can only absorb so much thc at one time.
Btw a nice tip to getting higher, when you exhale a hit, don't blow it all out in one long cloud. Exhale for a second, inhale, hold for a couple seconds, exhale a little, inhale, hold, you get what I'm saying. Try it the next time you only have a bowl or two left and you need to make it stretch.