A must? No. But you really should use a torque wrench. Especially on the M3, which is very sensitive to any vibration-causing irregularities.
It's not difficult, it's not expensive, it doesn't take much extra time, and you have the satisfaction of doing the job right.
I have accepted a new position at Tire Rack and am no longer in the sales department. email@example.com
is available to assist with M3 questions.