It doesn't matter so much with field points or target points, but when you put broadheads on the arrow... The bigger the broadhead and the more blade surface you've got, the more fletching you need. A big 2-blade, unvented broadhead needs a lot of fletch. A small 3 or 4 blade head with vented blades can get by with less.

That's assuming your arrows are correctly spined and the bow is tuned to them real nice.

Even mechanicals have SOME exposed blade surface so, IMO, they need a bit more fletch than you can get by with on field points.