People usually make judgment on the first impression of the person and decide very quickly what kind of person they are and if we like them or not. Even if it is a common thing, it can be a bad habit since it may lead to the wrong impression.
One the one hand, immidiate impression of the new people may help to bit understand their characteristic and just imagine what kind of people they are.. Additionally, people may understand if you will suit each other in the future. By this little judgment most people decide if they want to build the relationship or it is better to them to stop after that first met.
On the other hand, quick judgment may result wrong decision. In the first met people might be too polite or reversely be at the bad mood, which may confuse their real character. That’s because people often can not open themselves to the new people in the first meeting, so if we don’t give some time to them we may mistake about them. For instance, I heard many stories from of friends that at the first met they thought that they will be never be friends or some of them were even with a bad opinion with each other. However, after some time they become friends, so quick judgement may lead to wrong impression since it depends from the mood of that day.
To conclude, it may be fine to judge people to imagine them, but it may be but habit since it is not always true. Giving some time to people may improve their confidence front of new person.