skribs
Grandmaster
I did Tae Kwon Do in my teens and I am nominally a Black Belt (Yes I know that's not saying much). In TKD we did our Poomsae in low stances, but in sparring there's hardly a hint of it. Didn't think much about it then, but now it's really puzzling to me why we would do our forms in a way that had little relevance to how we actually fought.
Because sparring and fighting are two different things. Even combat sports like MMA are different from fighting. There's different rules (none) and different objectives (points vs. survival). In my TKD class, we do sparring with the faster, shorter stances, but our self defense techniques (those that incorporate only blocks and strikes and those that incorporate grappling) we use lower stances for better balance and better power, at the cost of speed.
Plus, if you're paired with an 8 year old and are doing a grappling technique that involves stepping under his arm, you need to be good with low stances! (Usually we get paired with people around our belt and/or size, but every once in a while you're the odd one out...)