Well, I'm not saying that it's a necessity. Usually, it's not a necessity to hold or attend those events in the first place.
But that does not mean that people don't deeply want it. I've been part of the orga team for a larger event before and that was our biggest concern: If anything happens that makes it impossible to hold the event, how in the fuck do you tell people to not come?
We did have a whole homepage specifically for this event and, to be fair, the answer was still generally that you don't. People won't subscribe to your RSS feed or regularly check the webpage. Unless a catastrophe happens, you have to keep to the time and place. But if we could reach even just 20% of people in case of a catastrophe, that would have still been massively helpful.