wow...broad question my friend. And, welcome to the forum.
Different stances in WC and when to use them is like asking what is the letter "A" and how often is it used.
WC forms (to me at least) are like learning an alphabet. Period. Where and when and how I choose to use a letter or letters is entirely up to me and the situation I am in.
Same goes for stances...which are just "letters" in the WC "alphabet"