One of the most obvious reasons people date is to find out what interests they share with the other person. The saying opposites attract doesn't hold much weight in the dating world. Each person should have their own interests, but if two people hate the activities the other one likes then they'll never find anything to do together. It also limits what a couple can talk about when interests fall on opposite ends.
Life goals may not seem important at the start of a relationship, but soon the couple should know what each person wants. Both short-term and long-term goals matter. For the short term, couples will want to know if both people want an exclusive relationship or if one prefers an open relationship. This in itself can make or break even a casual relationship. Later on if the relationship gets serious, couples should know what they both want to do in life. If a man wants children and a woman doesn't, this will cause stress on the relationship later on.
Views on everything from religion to politics may play a part in a relationship. The important factor is not so much what each person believes, but how different these beliefs are and how devoted each person is to the beliefs. Two open-minded people from different religions may have no problems in a relationship. On the other hand, two people whose religions teach they should not date outside their religion may feel guilty or have trouble with the relationship.
Dating also shows someone what the other person acts like on a day-to-day basis. At the start of a relationship, a person may appear sweet and caring, but over time red flags can appear. An unhealthy relationship often shows more and more signs as time goes on, and dating allows people to watch out for these signs. Disrespect, emotional abuse, jealous tendencies and a person who angers easily and becomes aggressive are all red flags that signal an unhealthy relationship.
Finally, dating allows two people to judge their physical attraction to each other. Physical attraction alone will not make a healthy relationship, while a good personality alone does not guarantee happiness either. For a relationship to work, both people need to find the other interesting and attractive at the same time. Days may come where one person doesn't quite feel the spark, but it shouldn't go missing permanently.