Originally Posted by gabbah

If you train with lowkicks I would definitely advice that yes, square off your stance a bit. I do know that kickboxers (american style) that don't train with lowkicks do have a more bladed stance as seen in the video, because you show less target to your opponent.
If you square up you should notice (after a while) that your roundhouse and right cross are easier to throw and land harder.
Using the more bladed stance will give you problems once your opponent starts lowkicking you... like turning you sideways even if you block the kick and so on.

That beeing said, the more bladed stance makes your sidekick and spinning back kick faster.
On the other hand, the more square stance makes your sidemovements faster, which means a person performing a spinning back kick that is a little too slow can be countered in a devestating way by sidestepping the kick and then onloading punches and kicks while he's still regaining his balance from just having missed the kick.
Knowing both stances and how to fight from them is even better. Then you can alternate between them and confuse your opponent.