Use of the left leg down not only helps with stability while at a stop but also frees up your right leg for your rear brake........"your rear break is your best friend at slow speeds". Hope this helps. Once I learned only my left leg goes down, I didn't find myself alternating between each leg and enforced a good habit that comes second nature.
Good to know! I honeslty thought that your left leg was supposed to be up so that way you can be ready to shift when the light turns green! But then again, I am a newbie and haven't even taken my training course yet. I guess I'll learn everything soon!
Oh and btw...is it just me, or with her wearing the green shell backpack, doesn't it remind you of the turtle riding the motorcycle in Mario Kart?! Lol!