I'm a veteran musician and a novice dancer. I think it is important for dancers to understand something about music. "1 2 3 a4" communicates one thing, q q q aq communicates a slightly different thing. I was fortunate enough to spend some time with an instructor who insisted on going over steps multiple times, one (or more) time "counting" quicks and slows, one (or more) time counting the beats that a musician would count ('and' and 'a' are not the same, as samba dancers know), and another counting the steps in a phrase, where the confusion about the number of beats being different than the number of steps gets resolved. They are all invaluable. Must say, though that '3 a4, 3 a4..' would be baffling, I think.