I think it was in one of John Kells' classes that someone asked about breathing.
Good Idea was the answer.
Some people co-ordinate the in and out breath with their postures.
I'm personally not in favour of this approach.
Let the breathing be natural. I feel that you will otherwise create tension in trying to combine it with movements.
Whether you move fast or slow, the breath will follow naturally. I think it is more important to remain relaxed, lively and spirited.
Of course opinions vary :)