What is it exactly, and what are the benefits???

 

It's a metal-oxide coating that's put onto something like a header, by flame-spraying or some other processes that are not easy to DIY like painting. It's already an oxide so it won't rust. Tolerates much higher temperature vs. paint. But since it's a coating like paint, someday the metal underneath can rust. The coating on my DC header looks like a satiny silver color.

Or maybe you were talking about the glossy white ceramic coating that's on a cast-iron bathtub??

 

i've heard that people get bottom ends heads, misc parts get ceramic coated. i would think it's because it stands up better to pressure, heat etc.... just wanted to know what's exactly behind the theory of that.

 

There are hundreds of coatings (ceramic is just one TYPE) available, coatings mainly help against wear and heat stress.

 

pistons in avatar have a thermal coating