1. An electrical ground and a RF ground are usually two different things. A ground rod gives you a pretty good to a great ground depending on the electrical resistance of your soil. Multiple ground routed radials/counterpoise give you a better RF ground than using nothing but just a ground rod. Look to DXEngring for a good write-up on ground radials.  2. Most modern internal (to the xcvr) antenna tuners will tune or match the impedance mismatch between the HYBRID/coax line and the xcvr's impedance, which is usually 50ohms. However, if there is a mismatch there will be RF floating around on the coax, call it common mode , or call it high SWR. If you put a SWR meter between your output from the antenna tuner and the coax feeding the antenna you will see it as reflected power and SWR. If the reflected power is high enough, you will see it affecting electrical things in your house or other houses nearby, like TVs, radios, dishwashers, clotheswashers, etc. If you use an antenna analyzer you can see how you can reduce this reflected RF thru hanging tuned (20, 15, 10 meter) radials and ground routed radials/counterpoise.

Hope this helps, 73.