Usually before exercise (as my heart rate got a little high during exercise when I was nervous, and I got palpitations) or when being stressed because it had a great effect preventing
panic. My
panic attacks stopped completely when taking
propranolol, and I never had a racing heart.
So, propranolol has often great effect on the fight/flight response. What it doesn't work against (at least not in my case), is that nagging, uncertainty-like kind of anxiety.