For most modern inkjet printers, there's a simple reason: there must be ink inside the printhead at all times[1] or some of the nozzles will dry out and clog.

For most modern inkjet printers, there's a simple reason: there must be ink inside the printhead at all times[1] or some of the nozzles will dry out and clog. [1]: https://superuser.com/questions/409473/how-to-print-in-black-and-white-when-a-color-ink-cartridge-is-out-of-ink https://superuser.com/questions/409473/how-to-print-in-black...