is slider hitch really needed with standard box? (6'5")

I was told by the dealer a slider hitch would be necessary for my 6.5' box. Didn't question the advice. Never have checked to see if the 5er would hit the cab or not. When I know I will be maneuvering in and around some tight spaces, I will take the extra 30 seconds and slide the hitch first. The last thing I want to be doing while backing my 5er in a tight spot is checking my cab to see if it will be okay too.