A side-angled fighting stance presents less of a target to your opponent and puts both limbs on that side in position to shield the torso and head from blows.

http://chinesemartialstudies.files.wordpress.com/2013/07/bru...

https://www.balazsboxing.com/thegym/boxingbasics_stance.htm

If you want to move in that posture, you either have to shuffle sideways, or alternate sides as you move.