Straight-offset or helical is absolutely vital to spin the arrow with broadheads. Helical is best, always.Helical does slow the arrow down more so gives the arrow a little more arc, but not noticably so at normal hunting distances. Weight of the arrow and momentum will affect this more. Lighter arrow slows down quicker, but again, not noticably so at normal hunting distances.

Straight fletching is OK for target or 3D any time broadheads are not being used, but again, slight offset or helical has proven to be better.

The type of fletching, staright-offset or helical, is not quite as important as proper arrow spine and FOC. Actually a combination of all three should be considered for best accuracy. Then proper bow/arrow tuning. The better a bow is tuned the less work any fletching has to do.