That's when you partied too much over the holidays and the pants need to be expanded. Can be avoided, of course
Well, think about it this way. If all you have is delta one products, you can do simple P&L predict using delta only and it would be good enough. If you have an options book, you can go further and predict p&l based on delta/gamma/vega, but if you want to can add other risk metrics (e.g. you might feel like adding dVega/dSpot and dGamma/dSpot if you have a lot of skew exposure) and make it more precise.
Dgammadspt measure change of skew? But the amount is so small what about dgammadvol? Which measure measure the shift of skew?
I was just giving an example that you can arbitrarily increase the precision of your prediction by adding more derivatives. Your mileage will vary greatly.