Depends where you are riding
I noticed you are in MA from the previous thread. If you ride places like the Fells you probably don't need one. At rocky places like harold parker, lynn woods, vietnam, you do. I broke off a lot of teeth on my big ring before I took it off and added a guard on a dual ring setup. I have xtr cranks, and with the XT's I am sure all you have to do is remove the outer ring and screw in the guard (provided you get the correct bolt pattern) Then you can always change it back if you are riding more Xc areas. I found I was never using the big ring anyway and I wanted the extra clearance of getting a smaller bash guard.