Counting Breath and Breath Theory
Counting breaths ask the mind to occupy itself with counting while the physical familitates the breath.
I prefer to teach 4 part breath as opposed to 3 part breaths because of what gets cultivated when you hold the breath out.
Differing the distribution of counts will either excite or calm the body. When your exhale and hold is longer it stimulates the parasympathetic system to rest and digest. When the inhale and hold is longer, it stimulates more activity.
Varying the length and intensity of the breath also contributes to energizing or relaxing breaths.