Practicing your facial expressions is hardly tactical training
Respectfully, that's just untrue. Your face is the part of you most people see first, and will be a major factor in escalation or de-escalation.
You should ALWAYS be mindful. An instructor I know says, "the real self-defense begins in the American legal system." Since we know that's the case, we should also know that our demeanor may be that final deciding factor on whether a grand jury returns a "no bill" or not.
John