I'm with Rob in that my decision to use mechanicals has absolutely nothing to do with their flight characteristis and everything to do with their cutting diameter and the damage they inflict. They simply do more damage than the fixed blade heads I've used. I have consistently better blood trails and if I have to follow them they are shorter. These are not statements true of every mechanical against every fixed blade, just my observations that have lead me to use mechanicals.
Basically you could say I'm lazy and don't want to track the deer, just walk up to where I watched it fall over.