Do I ever NEED to remove the angle grinder guard?
I have found removing the guard to use a product like this makes sanding welds flush extremely quick and painless.  At this point you are just using an angle grinder as an overpowered sander, so the dangers of using an unshielded grinder are reduced.  

The danger of the grinder comes from applying force to the edge of a perpendicular spinning disc, which creates the possibility that some piece of material will be caught and flung back to the operator, which is why the guard should be positioned between you and the tangent of the disc you are working on. If you use a disc like above you are directing the force perpendicular to the spinning disc so the forces are not as great.