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

I assume it depends on the front of the 5er.
I have had a 2006, 2009 and now 2012 silverado with the short bed.
I had an 37' 06 Sierra and now a 39' 2012 sierra. I have a slider and have never needed to use it. The Sierra's front cap is rounded and I can go 90 degrees and not hit. Very seldom do you actually go a full 90 degrees. I did it just to check. I have clearance. I have heard of people that need it. It also depends on the pinbox. most newer 5ers have a longer pinbox than they made back in the 80's and 90's.