RSVP
Perfect solution for those who don't #RSVP
All #weddings and #events experience late to no RSVP responses from invited guests.
I have seen couples opt to have a table seating designed for the #ididntrsvpbutcameanyway guests to be seated. It may be perceived as poor taste but it mitigates conflict with interrupting current seating arrangements that were already confirmed.
Always respond to a RSVP invitation date provided.