It's expected to RSVP to important events.
Julie receives an invitation to Sue and Joe's wedding and places the invitation and RSVP card on her desk for later.
Julie wants to her friends get married.
Julie remembers about the RSVP  but won't have time to mail it back, so she calls the bride and lets her know she will be coming.
Julie forgets to send the RSVP card back but shows up to the wedding anyway.
Julie goes to the wedding and has a great time and has lots of pictures to remember her friends wedding.
Julie forgot to send the RSVP card back so there is no spot for her at a table, and she has to leave.