Why is a structured RSVP better than guests just texting me yes?
A text tells you someone intends to come; it does not tell you reliably how many, or with which meal needs. An RSVP collects the confirmation, the plus-ones within your limit and the meal note as one record against their name, which is what a caterer or seating plan actually needs. A yes in a message you have to tally by hand.
Can guests bring someone, and how is that controlled?
You set the limit when you build the invitation, and the reply honours it. A guest names a companion only up to the number you allowed, and that person is added to your count. This applies the same rule to everyone and keeps extra heads known in advance rather than discovered at the door.
Does the RSVP capture dietary needs too?
Yes. Alongside confirming, a guest can record a meal preference or an allergy in their reply. That turns a single headcount into a per-dish one, so weeks before the day you can give the kitchen an exact number for each option, including the guest who cannot eat most of them.
When will I actually know who is coming?
The list builds live as replies arrive, so you are never waiting on one final tally at the last minute. The guests who have not answered are simply the names still unchecked, and a reminder goes to exactly those people, so the count firms up while there is still time to plan against it.