Too much humidity can harm your home and some of the things in it.
So, sometimes you may want to use a dehumidifier.
Many times a basement can be very damp. It may need a sump pump and/or a dehumidifier. When choosing a dehumidifier for a basement, it's important to choose a basement dehumidifier, and not just a home dehumidifier.
A basement dehumidifier will be calibrated to dry out the cooler basement environment, as cool air is harder to dehumidify than warm air. A home dehumidifier set to dry a basement that's rated to remove 60 pints per day in a 70 degree Fahrenheit home may only remove 8 pints per day in a 55 degrees Fahrenheit basement.
Another situation when you might want a dehumidifier is when you have items that are valuable to you and which could be harmed by mold. This could be anything from important paperwork, valuable artwork, cigar storage or things that could rust or tarnish.
High humidity can make hot weather less comfortable. Some people run their air conditioner on relatively cooler days for the effect of reducing the humidity.
By making warm weather more comfortable, when you lower the humidity you can raise the temperature of thermostat without decreasing your comfort level. In some cases, this may reduce your air conditioning bill.