In most cases, there will still be toner powder in a cartridge once the electronic counter chip reports it as empty. This is because the chip does not actually use the actual amount of powder used per printed sheet of paper as a basis for calculation, but in most cases only takes an average (e.g. 5% coverage) and simply counts down the number of printed pages from a stored value. What this means for you is that if you exchange the old chip (with an empty page counter) for a new counter chip (with a full range again), you can continue to use the old, supposedly empty cartridge until the last bit of toner powder has been printed.

You can now continue printing until there is only so little toner powder left in the cartridge that the print quality deteriorates. The advantage for you is that you can decide for yourself whether a little paleness in the black is still acceptable and when to use a new cartridge. As soon as you decide that it is time to change the toner cartridge: Keep our (probably only partially empty or counted down) electronic chip for the next (according to the counter) empty toner cartridge, so that you can print it completely empty too.