Why swim slow and smooth?
When you've mastered a skill, you can execute it fast or slow at will. That is true kungfu, btw 功夫 means skill literally, and 师父means a kungfu master. Why do it slow? Because of the way our muscle memory, timing between static and dynamic balance, body coordination between cardiovascular circulation, if you can only do it fast to stay afloat and not slow, you have not learnt dynamic balance. If you are breathless and higher heart rate after a relax swim, you have not learnt breathing coordination with your movement. That's a fact.
