As others have said, it will depend on the truck and 5er.
My first set up, a '99 Ram short bed and 1998 Dutchman 5er never needed a slider.
My next rig, an '03 Ram short bed and current 5er, needed it just about every time I backed into a site.
I had a Reese 16k Qwick Slide, and that thing was PITA to use, I had to drop the landing gear and remove most of the pin weight to get it to slide. I finally upgraded to a Superglide, which was great for manuevering, but it must weigh over 200 pounds, and was a PITA to get out of the truck.
Most things in life are trade offs. This is one as well.