For many uses, hard water does not cause any problems. Hard water is not damaging to your health either. In the domestic environment hard water is not very efficient for certain uses: for bathing, washing dishes and clothes, shaving, washing a car, etc.
There are a number of negative effects to hard water, for instance: soap does not mix with hard water very well, when hard water is heated the hardness minerals can plug the pipes and hardness minerals often interfere with industrial processes. That is why hard water is often softened.