This is standard practice, in my experience. People would often join the groups I was running here in Nice to say they'd be around in a couple of months, just wanting to say hi before they arrived. They'd always get a warm welcome and as much information as they wanted.
So it was with some surprise that I received the following round robin email from the organizer of a discussion group to which I'd subscribed:-
Members can RSVP Yes and either change it to No or not show up once only. If this is done twice they will be unable to RSVP for any Meetups for three months following. This is now apart from one inactive member being removed and banned for at least a year every month. I am able to check through the site members RSVPs. This is so that members take their RSVPs seriously.