We learn early on that albeit we teach students to say 1,2,3 4,5,6 that we (pros) never dance a waltz in 3's. Because of the swing (glide) of the first and second steps, we dance 1,2 3,4 with an invisible weight change which would normally be the 3. To help me understand this, a music/dance teacher showed me once that a waltz, though written in 3/4 time is phrased in 8s. Listening to a waltz, one can count 123 223 323 423 523 623 723 823 and notice the phrase change. It doesn't happen on 623 as one might expect. Of course, all songs are different, and there are those that will blow this theory out of the water, but we still dance, even those, in 2s phrasing 8s.