I think for most applications, the wiggle between the upper and lower is inconsequential for accuracy. However, if you are doing precision shooting with your AR and holding your rifle on a bench the via traditional method i.e. right hand on the grip and around the trigger and left hand under the right arm with your left hand gripping the end of the stock, you are going to lose some accuracy. This is because if you are trying to steady the gun using your left hand on the stock and the stock wiggles, then you can see why it may be more difficult controlling your barrel and thus accuracy.