Have you ever been to a concert where the audience is clapping during the song, but on the wrong beat? While performing “Come By Me” during a live performance, musician Harry Connick, Jr. used a clever trick to get his audience to clap along on the correct beat. The video explains how clapping on 1 & 3 makes the song feels like it drags, because it matches the intensity of the notes that are played. When you clap on 2 & 4, though, that intensity is more even throughout the song and so it feels like it flows better rather than a stop-and-go type of feel.
A different explanation of the same process.