Emails have replaced
wedding invitations for the most informal affairs, but by and large, paper invitations still rule.
I helped organize a wedding once where the wedding invitation had two boxes. One was to indicate if one or both of you were coming, while the other expressed regrets on the part of the invitee. There was one RSVP that did not have either box checked off, and one of them had both.
Was it an oversight? No. The two guests in questioned wanted to remain ambiguous. One was unsure, but then they could have written that they were waiting to hear about the thing that might prevent them from coming so that the bride and groom could make a judgement call when they submitted their count.
The other party was in for the drama. They wanted a fuss to be made over them. They wanted to be begged to please come, and otherwise create drama over "Will they or won't they?" In the end, they did not come, but kept everyone guessing to the very end. The family member who they were inseparable with RSVP's which led everyone to believe one outcome, but it really was quite the opposite.
If you are a fortunate invitee - RSVP - otherwise everyone will not set a plate for you.