Can I use a carpet cleaner on hardwood, tile or other hard floors?
Dad’s short answer: Generally no. Carpet cleaners lay down a lot of water and rely on the carpet holding it long enough to extract, and that's exactly wrong on a hard floor. For hard floors you want a wet/dry floor washer, which is a different machine.
Why it doesn't transfer
A carpet cleaner is built to saturate. The solution needs to reach down into the pile and dwell there, and the machine's suction is designed to pull water back out of fiber. On a sealed hard floor that water just spreads, and on wood any water sitting on a seam is a genuine risk.
The brushes are also wrong. Carpet brushes are stiff enough to agitate pile, which is not what you want on a finished floor.
For hard floors the right machine is a wet/dry floor washer — the cordless ones with a wet roller and suction that lifts the dirty water immediately. Different category, and one I've tested a lot of.
The exception: upholstery and grout tools
Most carpet cleaners come with hand tools, and those work perfectly well on upholstery, car interiors, stairs and area rugs. That's fabric, not hard flooring, and it's one of the most useful things these machines do.
Some machines offer a grout or tile attachment specifically. If yours does and it's designed for it, that's fine — it's built to control water and extract on a hard surface. Don't improvise one out of a carpet tool.
And a note that applies to both categories: check whether the tool you're about to use is meant for the surface. The single most common way people damage a rug or a car seat is using a stiff carpet brush on something delicate.
Dad’s Take: Carpet cleaner for carpet, floor washer for hard floors. The tools cross over to upholstery, the machines don't cross over to wood.