Please excuse my ignorance but could someone explain the benefit of having a + or - 5 percent on the Zebra settings? on the C300 say I was using 90 percent Zebra what would be the benefit of using 90 percent plus or minus 5 percent?

The 100pct (or 90pct) zebra is good for avoiding of luma overexposure, the 70pct (+- 5pct) zebra is good for correct exposure of faces (without chroma clipping). Try to learn more about RGB to YUV (YCrCb) conversion.

Yes and go out and spend time experimenting with the settings, don't tack it on at the end of a shoot. When you change the values, actually say (speak) the new settings on the cam mic for reference later.

View your results on various monitors to learn about this, most vary somewhat.

Cheers.

As was mentioned earlier staggered zebras allow you to gauge exposure across multiple surfaces through your viewfinder/monitor. You can set it up in any way you like, but the most common was as mentioned above to get skin and the sky dialied in.