Hi THawk and welcome to GotMead!
Yeast pitch rates and oxygenation/oxidation are fairly common topics, so you should be able to find some good info with a quick search of the forum.
In short, adding a lot of yeast means that the weaker yeast will give up early in the fermentation, spill their guts, and the other yeast will gobble (parts of) them up. Exploding yeast is autolysis, and it can lend a yeasty flavor to your mead that might not be what you're going for. Usually you need to pitch quite a lot of yeast to risk this particular flaw, but 10g/gallon is probably getting close to that level.
Oxygen is a pretty good oxidizer, you can probably tell that from the name. Early in fermentation the yeast will take up dissolved oxygen and use it for their metabolism. Once the mead is done and the yeast aren't doing anything, oxygen in the mead can cause chemical reactions, changing the color, flavor, and aroma of your mead. These changes can lead to something like sherry or Madeira, or on the other end of the spectrum wet cardboard or dank must. Usually neither of those possibilities is what you're going for, and controlling things to get one rather than the other takes some work. To see oxidation first-hand, pour a glass and leave it on your table overnight. It will not taste the same in the morning.