Penetration is increased because there is no fletching to pull through. The FOB pops off easy and marks the spot. A bare shaft will penetrates much deeper than one dragging a fletch through. Lots off data of this one, both on critters and targets. Pick FOB up of the ground for re-use.
Roving is where the FOB cranks over fletch for durability. I rove about once a week here in the desert which is very tough on vanes. I now use the same FOB over and over again. Even after 20 or more pass through shots, the FOB just pops off for re-use. I loose more than I break. Honest. I even break arrows before the FOB is replaced. There is no doubt that for me, FOBs are less expense. (well-in my case maybe not-four years of work and mortgage the house for this project).