They are cheap, machine washable and clean anything off of anything else gently, quickly and efficiently without expensive specialty cleaners including:

spills off carpet and upholstery, dried on gunk off of stove,built up furniture polish off of furniture, anything off of hardwood or laminate flooring, soapscum anywhere in the bathroom.

They can also be used normally to mop up kitchen spills (no more paper towels!), they’re great for dusting cloths (take that swiffer!), and will even pick up quite a bit of pet hair off furniture (goodbye rubber mitt thingy!).

As a side note they also get dirt off the dog really well when it’s wet and muddy.