Originally Posted by G.AUDI
PCV regulates crankcase pressure, so that the engine retains proper vacuum and doesn't over-pressurize and blow out the various oil seals in the head/block. Many people "delete" this system to varying degrees for various reasons (becuz racecar, to "simplify", because they got annoyed at it and hulk smashed it, etc) but doing that, you're just asking for sludge issues and the engine won't get a constant supply of fresh air circulating through the block, purging the oil vapors, etc.
EVAP is a emissions system, that recycles the fuel tank vapors and pumps them into the intake tract. Its a metered part of the fuelling system, so deleting it will cause lean conditions at worst, or increased fuel trims at best.
SAI is a stupid emissions component that helps to speed up the heating of the catalyst elements. It serves an important purpose from an emissions perspective, but won't affect proper engine running in any way, unless you leave the SAI port on the back of the block wide open, then you're an idiot, haha. The SAI is perfectly fine to remove assuming its done right. When the pumps fail, people often just rip them out, which is fine.
People LOVE to just rip these systems out willy nilly because their brains can't comprehend why there are so many lines and what they do. So rather than actually learn what they do and understand their purpose, they rip them out. The reasoning being, well my '55 ford pickup/'96 Talon/'99 Civic don't need this shit, emissions are for tree hugging hippies, and I'm an idiot, so it's all gotta go buddy!