People tend to define a person in a short time when they meet him/her for the first time. In my opinion, it is not a positive thing. I will provide the reasons for my viewpoint in the following.
The first reason is that it may make difficult for us to make good friends. When we give a definetion for a person quickly, it is usually based on the appearance. But People under different backgrounds may have various characteristics and thoughts, which may make us make a wrong decision on what kind of person he/she is. In this case, we often make friends with those who actually not suitable for us. Thus, we often feel lonely in our daily lives.
Another reson is related to the result that people may think we are not polite. If we often judge others without knowing them, it is easy to make mistakes when we are talking or working with them, which may lead to the result that others often feel uncomfortable or even offensive. In this case, we may be considered to be rude. Moreover, it makes more difficult to connect with others becuase of the misunderstanding with each other.
According to the above evidence and analysis, it is not recommened to decide what kind of person someone is without knowing him/her and whether we like him/her. If we want to have more good friends and better experiences when connecting with others, it is best to know more about them and then make the decision.