For us, it would mean one extra step before I could RSVP. My kids to to school at a charter school, so the students come from a rather large geographic area. A positive response depends on both the time and the location. If I have to drive 30-45 minute to get to the venue (has happened), there are some days where that simply doesn't fit the family schedule. And if I have to call first to get the location, well, frankly, that would be mildly irritating and would result in my putting less effort into making it work for my kid to attend.
So, my response is, if you know most families live close by, it's probably workable. But if you have people who will have to come a long distance, I think you're going to end up with more back-and-forth with each family before actually knowing who is coming. And you might end up with fewer people overall because of the hassle.
But maybe the trade-off is worth it, if it means you know who will be there.