Last a year a teacher was accused of not teaching his students properly because he liked to tell private stories in the class from time to time. However, I think such familiarity between teachers and students is needed. It is helpful for students to foster familiarity and camaraderie with their classmates and teachers, and not just only focus on academics.
First of all, when teachers treat theirs students intimately, students can improve their performance. This is because they feel comfortable with their teacher so that they may be inspired to do beeter in the class. According to a research conducted by a Korean Education Ministry, students in the class that a teacher talk some private stories related to the lesson usually concentrate more on the class rather than those whose teacher focuses on just teaching. Further, because the students often interact with their teacher, their study performances are much higher than others.
Secondly, I believe the closeness between teachers and students can be some help for students' future. Students can easily share their concerns with their familiar teachers. And, the teachers give them some advices. For instance, when I was in middle school, I was not able to decide whether I should prepare for enrolling at foreign language school or not. I needed some help, but my parents and friends did not know well about it. So, I requested some advices to the most intimate teacher with me in the school. She provided me with lots of information for admission at foreing language high school, and also afforded me man advices about the future and life. Unless there were at least one teacher familiar with me, I might wander how to do at that time.
These are the reasons why I think it is better for studnets that teacher should be familiar with their students. I also beliee that teachers reminisced by students even after graducation are the familiar teacher, not just "teaching" one.