Unfortunately this means less than you'd think. See other comments on this thread on the subject of accuracy. Also, from my understanding, the current (still wanting) state of accuracy is the result of large improvements during just the past few years. Prior to that, CGMs were still prescription medical devices used by Type 1 diabetics to say alive.

And more unfortunately, it has been my experience that information about managing blood sugar given to diabetics by doctors is almost uniformly quite bad (I've received the same sort of overly simplistic, misguided instructions from 4 or 5 different doctors myself; now I just nod and let them finish speaking). As a result, nearly every other (non-engineer/scientist) diabetic I've been met has very bad numbers (A1C: three month average blood glucose)—as I would have too were I to follow my doctors' advice. Instead I have very good numbers which are a result of research and reasoning I had to do myself.