RSVP, as one may learn in Paddington Takes the Air, stands for the French expression "répondez, s'il vous plaît", meaning "please reply." This means that it is redundant to say "Please RSVP."
Incorrect: Cocktails at my house Friday at 8. Please RSVP.
(In fact cocktails are always served at my house on Friday at 3, and I already said please.)
Correct. CSPP conference on Monday the 11th. RSVP.
(In fact there is a conference and if you're coming we'd like to reserve you a spot, so let us know. While we're on the topic, let me mention again that this is mostly a glorified playdate for any mom and kids who otherwise plan to be bored that day. I will not be counting children and making personal judgments on the basis of my accounting on that day. Or any day, as I have attempted many times to explain.)