I like to change teams once a quarter. I feel like giving them nine weeks together gives them plenty of time to get to know each other and get comfortable. At times, I feel that my team configurations are so well suited for the students that I hate to change them, but even though I would like to keep my class the same, changes are necessary and beneficial for them to build new relationships.
There have been instances that I have had problems with a seating arrangement that I had to change unexpectedly. Before I move my students I always take academics into consideration along with behavior and personality. By the first couple of weeks of school, I have a great feel for how my students are and how they will interact with each other.
During the rare instances that I have had to move a student due to incompatibility, I re-evaluate the entire seating situation and take into consideration the dynamics of the other students.
Also, every quarter I keep track of my seating charts so that my teams are never the same. I even try to make it so that no two students sit at the same team all year, even though sometimes that is not possible.