With counterfeit cartridges the printing behaviour may change, leading to the almost-invisible tracking dots on each page that encode the printers serial number

With counterfeit cartridges the printing behaviour may change, leading to the almost-invisible tracking dots on each page that encode the printers serial number, the cartridges serial number, time of day, etc to either become too visible or too invisible. Also, with different ink your printer might print content with a different color profile, so it won't look the same, and it might need to clean the printing heads more often (and the cleaning tech for that is often only designed for a limited amount of uses). But while all these are legitimate reasons, projects like Instant Ink show the true reason is to just turn the printer into a subscription product: buying a printer at a loss, and making a profit with every page printed.