Lighting, Light Fixtures, Ceiling and Exhaust Fans - EMT Grounding Question

I also have a basic question about grounding ... I just ran some new outlets in my workshop. I ran 12/2 on a 20amp circuit. For a pair of receptacles on one of the basement walls I use EMT ... my set up has the 12/2 coming from the overhead joist into the EMT conduit (I have a plastic bushing on the end) down to a receptable box out to more conduit to the next receptacle box. I am actually running two circuits in the conduit. I have all the grounds connected - and back to the panel ... but I have seen pictures where in addition to the continuous ground provided by the wires themselves, there is a pigtail from the grounds to the receptacle boxes also. I am curious what that connect would do - and whether given my "free standing" conduit set up (ie the EMT does not go to the panel) whether it is meant to "ground" any current if one of the hot wires inadvertently gets lose in the receptacle ... or is it something else?

Basically, everything metal needs to be grounded if wires run in it or through it. So yes, you need to ground it. If you ground the metal box, the conduit will also be grounded since it is in direct metal-to-metal contact with the box.

There should be a threaded grounding hole in the back of the box. Buy a premade grounding pigtail, attach the green screw there, and attach the other end of the pigtail to your grounding wires.