In what ways isn't it relevant? If you've moved through the expanded species, as well as third species, you should be writing smaller values, and of unequal durations.
Then, variations on species are variations on melody or rhythm. Counterpoint does not have to sound like a fugue, and I still think the technique is a must. As far as the rules are concerned, I don't use them :P Though understanding beat subdivisions helps writing multiple melodies/rhythms (for me).