The main things that spring to mind for me are that the steel tanks remaining clipped will add tension to the chest d rings which could make them more difficult to use, especially as bungee is pulling the cylinders back. And secondly, the clips being left on will prevent the bungee from pulling the cylinders fully into their best position.
The clipping to chest is only need for supporting cylinder weight out of the water, in water it's not exactly difficult to unclip a couple of double enders and reclip then at the end of the dive. This keeps everything as optimal as possible.
But that's the beauty of SM, it's actually acceptable and encouraged for divers to use their heads and decide for themselves their own preferred configuration, not just blindly follow a "standard" one.