Manufacturers want to provide a product that produces reliable high quality prints. That's why the toner low warning comes up very early, so that there's no chance that your important documents look unprofessional due to low toner levels.
As a consumer, naturally, you can almost always ignore the warning and use the toner until you can't even read granny's apple pie recipe anymore.
I spent some time maintaining a fleet of printers, among other things. Toner cartridges streak when they are near empty, and can be restored by shaking them, for a time. Shaking them more and more as they near the end. I can understand why you’d want a cartridge to report “empty” before it starts streaking.
I don’t really care about a bit of wasted toner, though. What I really want are more durable mechanical parts (gears, etc) and a ready supply of replacement parts like fusers.
I also wonder how the printer counts its toner “empty”. If it’s just a page count, surely it wouldn’t be accurate. I know that you can measure page coverage, but I wonder if they actually do it.
I’m also sure that they have no incentive to make the “empty” threshold more accurate.
This is being a bit too generous. If that were the case, they could provide a warning about print quality instead of just saying that the toner is low. But then people wouldn't be as compelled to needlessly buy more overpriced printer supplies.
As a consumer, naturally, you can almost always ignore the warning and use the toner until you can't even read granny's apple pie recipe anymore.