Been pondering this a bit... yeah in every style I've ever done we aim to keep the head level whilst moving through stances (or moreso when moving in and to the same stance).
While the directive is usually to keep the head level, I don't really think that's the reason for it, which is circular. I sort of feel it's to reinforce and keep your connection with the ground. If you come up and down there can be a tendency to lose that connectivity, which is something you really need to keep when moving. Not only for balance reasons but for if you need to change direction rapidly in your advance too, or even if you are suddenly hit with impact you need to keep your equilibrium.
Another thing may be also to maintain "potential" throughout your legs. If you come and straighten out you lose that potential and readiness. You can maintain that bend and keep that potential energy like a spring ready to uncoil rapidly.
Just some thoughts!
While the directive is usually to keep the head level, I don't really think that's the reason for it, which is circular. I sort of feel it's to reinforce and keep your connection with the ground. If you come up and down there can be a tendency to lose that connectivity, which is something you really need to keep when moving. Not only for balance reasons but for if you need to change direction rapidly in your advance too, or even if you are suddenly hit with impact you need to keep your equilibrium.
Another thing may be also to maintain "potential" throughout your legs. If you come and straighten out you lose that potential and readiness. You can maintain that bend and keep that potential energy like a spring ready to uncoil rapidly.
Just some thoughts!