Why should anyone feel the need to do so? There are two divergent reasons, which are the basis for the two distinct types of double dating.
There are people who are eager to get married. There are quite a number of reasons why someone may consider that double dating would be a good idea. This kind of double dating involves the person consciously pursuing dating on parallel tracks to increase their odds of a successful outcome.
Then there is a second type of double dating when a person is seriously dating someone but is unsure whether this is “the one.” So dating someone else may help to clarify whether this person is really suitable. This second type of double dating was not pre-planned intentionally but is a response to a predicament.
The problem is that double dating goes contrary to the essence of what you are trying to do, which is why it generally does not work. The core of dating is commencing a process through which you become increasingly absorbed in a single person.
For the dating process to achieve its purpose it must transition from a continual focus on your own interest to a growing attachment to the other person. This kind of emotional bonding is only possible with one person.
Dating two people increases the chance of failure with both people – completely the opposite of what this double dating plan was supposed to achieve.
There are several other considerations. Please read the full article for more insight into this topic.