Inkjet printers charge/clean their print heads during start-up, cartridge/head changes and in intermediate head cleans during long print jobs and actually pump ink out the nozzles into the waste discharge tray (opening up defunct inkjets and examining this discharge tray will show that at least 1/3 of the ink run through the printer during its lifetime ends up in this discharge tray).
Fortunately, Laser printers work a little bit differently in one important way.
Monochrome Laser printers go through a start-up routine to check for jams and make sure the paper path is clear. While the parts rotate, toner is circulated through the mechanism that transfers it to the drum, but because the drum has no charge on it, no toner gets transferred to the drum and gets returned back into the cartridge to await an actual print job where it actually gets used.
EDIT: Color Laser Printers have a slightly different problem. They have to keep four colors in registration (synchronize where the colors land on the paper fed through the printer) and therefore do a calibration routine which will use toner in this process.
If you have an art department, and they still have the stuff, a piece of rubylith tape does a good job of dimming out those over-active LEDs.