If I were designing my own printer and wanted to both fully utilize ink cartridges (maximize efficiency) and also be able to print absolutely perfect pages when necessary, it'd be a simple solution: two cartridges. One that is potentially "low" and is used for printing low quality stuff, and one that is guaranteed to be full and is used for printing high quality stuff. Presumably, the "low" cartridge would run out first, and then you just move the existing "high" slot one down and put a new cartridge in the "high" slot. If instead the "high" one ran low first, then replace it with a new one and queue the old one to be the next "low" one when the existing "low" one ran out.

Or something. :)