Insect and Spider Identification: CLOSED: What kind of insect/fly is this?, 2 by Jubilada

Jubilada wrote:
This insect/fly was hiding on a leaf of chard picked from my community garden in Palo Alto, CA yesterday morning. I stored the chard in a plastic bag in the fridge overnight before getting around to cleaning it. Lo and behold, here it was on one of the leaves, and it had survived, even after an initial dunk in a bucket of water. I took it outside and let it go, after taking a couple of pictures. It was around 3/4-1 inch long, as I recall. I'd be happy if anyone can ID it for me, and ... is it a "good bug" or a "bad bug" and do I have to worry about infestation???