It really does depend on the company and the style of student you are teaching. Realisticall i like the feel o the tie and ****** bars... makes me feel like i've earn't what i'm wearing but admittily living in australia it can bet pretty hot... general rule of thumb is that if it is hotter then 30 degrees the tie can come off.
I think the professional look instill more confidence from the student in the instructor.. especially at the ab-initio stage, and the professional look as a commercial teacher gives the student something to look up to