You un-tighten and then slide your handlebars through the side, more efficient when constructing a bike from frame upwards.

 Seems sensible enough, but i can see alot of people getting pee'd off from scratching there new shiny bars this way, not sure whether if its already like this but smoothing and rounidng off tue clamp edges would be a good idea.

 I know what you mean about it scratching handlebars passing through the clamps, but I'm pretty sure they have already thought of that, along the design process cancelling out any faults that would not benefit the user/customer.