One of my favorite comments chains here was was something to the affect of:

Commenter posts a nice summary of how ZFS will try a quick compression algorithm to see if a block is even compressible and then try other more expensive ones to achieve better compression.

Another commenter asks how they know that.

First commenter replies that they wrote the code for it.

Nothing more than a ZFS user (to some extent my company relies on it even) here, so I just try and color inside the lines, but I'm ever impressed by it.