I had another brainstorm. With respect to rhythms where #3 is relatively loud, which describes most rock: I think it's actually a bit of a trick. It causes the

I had another brainstorm. With respect to rhythms where #3 is relatively loud, which describes most rock: I think it's actually a bit of a trick. It causes the song to sound faster. The reason is because the snare or whatever on #3 is perceived as being incongruously loud, too loud to be an echo. Which gives the impression that it's a second main beat, splitting the measure into two halves and making it sound like 2/4. Having said that, it might also make sense to consider it an echo of the bass drum. You could remove the snare and leave the bass drum and it would sound ok. If you tried to remove the bass drum and leave snare on #3, it really wouldn't sound right.