I don't mind +/- 5 lb fluctuation. I do mind when the +/- 5 lb fluctuation begins trending upward. So I weigh every once in a while. My weight recently began fluctuating between 184-189, when it's usually 170-175. So...yeah. Lord knows that ain't muscle.
I appreciate the intentions of Griff's post. Just keeping a smart eye on the scale (with proper context) works for some, doesn't work for others.