In Fluid templates only values, assigned by the extbase controller, are available. There are cases, in which these values are not sufficient and other data is needed. The “missing” data can be provided through data processors.
The first two layers of the TYPO3 performance onion where about quite common topics valid for every website: (browser) caching and frontend optimization. The next skin level is about TYPO3 rendering and what TYPO3 integrators can do for the performance of the website.