Yes Joel, you take it when you need it.
You would not believe how many artists, speakers, musicians etc that use it on stage to keep it together. Basically it put a bit of brake on the internal throttle, avoiding unpleasant heart beating and sweat dripping from your forehead. Calms you down. And it works.
Edit: Hence, it does not work if you are nervous running a 400 meters dash!
At least, you won´t win.