I got started with HT about 3 years ago.. I think the idea behind grounding a wire or two up here is if we get enough snow the cows arent grounded and they walk right through it, one of my neighbors had this happen back in 2000. You probably dont need to worry about that much snow, but I would think that dry conditions may be a similar situation. I put 4 or 5 ground rods near the energizer and a few here and there in the far corners of the fence and run them to the grounded wires.
In regards to number of wires... the first fence i did was 5 strand.... 2nd from the top and bottom are dead.... the bottom wire dead is nice when i run the mower around and get hooked on it, i can just pull it off the mower... but thats about it... if we get enough snow for the cows not to be grounded, that wire will be buried anyway...
Since then I have gone with 4 wire on perimiter fences with the 2nd from the top being grounded...
Having one ground wire makes it easy for rolling out polywire for rotational grazing.... you can work the fence without killing the juice. hook a gate handle onto the ground wire while unrolling, and then hook it to the hot when you are ready.
They always say that the wire is the least expensive part of HT fence, and I would agree, but it doesnt matter to calves how many wires they go right through it anyway. Had one the other day go right through a run of fence that I have 6 wires 7" apart (keeps hogs in) with 9800 volts going to the hot wires... barely slowed her down... I can keep the cows away by stringing a polywire with no juice to it though...
probably way more than you were looking for...