I did forget to mention too that running the bleeds in the MIN position (rather than NORM or MAX) will also save a little bit of fuel. By going from MIN to NORM to MAX, we command more bleed air from the pneumatic system. Commanding more bleed air causes a reduction in airflow which results in decreased engine performance. The reverse is true where commanding less bleed air causes an increase in engine performance up to turning the bleeds off. However, there will always be a slight draw because the Q400 uses bleed air for airframe de-icing, so you can never turn ALL the bleed air off, only that part going into the air conditioning system unless you turn both engines off.
However, modulating the amount of bleed air used has the most direct impact on passenger comfort for all the fuel savings methods. Most pilots I fly with either ignore the potential fuel savings or come up with some sort of easy-to-remember system like 20 people or less use MIN, 21 to 60 use NORM, and over 61 use MAX - something like that.