Yes at the range. It's polite for other shooters and safety officers.
No during storage or transport, except air travel. Easy for TSA or people at the baggage check to see what's up. I don't like racking open the action in a crowded airport. More discreet to just point at the chamber flags.
Maybe if going to a range where I want the flag in when it comes out of the case or to a gun shop or something. This is also to be polite for other folks who may not know that I'm the only one professional enough...