It helps drive the gun, but everyone has to find the right position for them and their particular physique. I'd suggest you get out to the range and try a few transition drills... let the timer tell you what hand position works best for you, rather than relying on how things feel.
Also, 3-gunners with a vertical foregrip or AFG are definitely in the minority - most prefer an uncluttered handguard for more flexibility when shooting off props. Again, don't be afraid to experiment, but let the timer be your guide.