We often use MBPipe to perform compression operations that reduce the size of individual tile requests (and of course the MBTiles file as a whole). We also use it for other post-processing effects, such as sharpening imagery that got a little dull in the rendering process, handling the transparency of the World Glass tileset, or quickly creating alternate-color versions of tilesets like we recently did with Blue Marble. The documentation covers these use cases with example commands and full explanations.
This black and white NASA Blue Marble tileset was created with MBPipe, starting with the full-color versions of the files. ImageMagick was used to desaturate the colors as well as to adjust the levels for a higher contrast between land and ocean. More details on how to style maps is available on support.mapbox.com.