Positive Mitzvah to Judge

דברים פרק א טז וּש ְׁפַטְׁתֶּּם צֶּדֶּק
מכאן דמצוה עשה לדיינים שישפטו (רש"י כתובות ק"ו א')

T.T. The practical difference exists where an expert judge errs in a judgment. The judge would be exempt from payment of damages for the error, since the Torah commands him to judge. The Shach learns this concept from the verse שופטים ושוטרים תתן לך. However, that verse places a mitzvah on the community to appoint judges. But the main derivation is that a mitzvah applies to the judges themselves is from the verse above. (Look at T.T. in פרשת שופטים as to why the judges do not make a blessing on this mitzvah like on other positive Mitzvos.)