At this point roll printing machine manufacturer may be helpful to review the differences between offset printing and digital printing:
Offset printing involves applying ink from an on-press reservoir to rollers, then to a printing plate, then to a rubber blanket, and then to the paper substrate.
Digital printing involves the building up of an electrostatic charge on a drum to attract toner particles (dry toner or toner suspended in a liquid or oil), apply them to a blanket or belt, and then deposit them onto the paper substrate.
For the most part (and to a lesser extent with coated paper than with uncoated), with offset printing at least some ink seeps into the paper fibers as it dries or is cured with UV light.
With digital printing, most of the ink sits up on the surface of the paper.
Offset printing is static. It cannot apply different information (such as different addresses) to each copy printed. Digital printing can.
For very short runs, offset printing is cost prohibitive (all of your money goes into preparation for the short press run). However, since there’s almost no prep work for digital, you can print as few as one or two copies of a digital press run.