When is weight distribution needed?

I'm certainly an advocate for WD/SC hitches in general and on my older 2500 and 3500 SRW trucks... But I'm well within the limits on this monster (new Dually) which doesn't even recommend WD in the manual... Taking 1400 lbs or so tongue weight hardly even squatted my truck (has a 5700lb payload) (yes I know payload and tongue weight are distributed differently) I was surprised they don't even make a 3" Weight Distribution setup... I'm just thinking it's an overkill for my situation this time around..