Soccermom.....like most other replies, I too have a slider hitch and have never needed it. Hitch dealers are quick to automatically say.."anything less than an 8ft box and you will need a slider." You can see from the replies that this is not true. But like most have said, you need to be aware of your particular situation, trailer design and box type.
What I did with our setup is I went to a large parking lot when the store was closed, and SLOWLY and carefully tested it, both moving forward and reversing. I now know how sharply I can back up and am much more confident when backing up. Having said that I am still very careful in case I am not on level ground, etc.
Bottom line... yes I probably could have gotten away without buying the slider, but now I have it, and should we ever encounter a dead end or as a previous poster mentioned, our Tom Tom steers us wrong and we have to maneuver a sharp U-turn, we may be happy to have the slider. The slider is way cheaper than a rear window replacement or a crushed cab corner, or having to repair the front of your rig.