Nobody wants coarse and hard carpets since it's not nice to touch. That's where water softeners come in. Water softeners are a carpet cleaners secret weapon.

Water softening systems remove minerals and deionize water to enhance the power of your chemicals and leave carpets feeling softer. They Eliminate mineral deposits from window and awning washing as well as upholstery cleaning.
Source: http://www.cleaningtips.com/tips/house/carpet-cleaning/water-softeners-carpet-cleaning.html