In case you hadn't noticed, EVERYONE in the A group gets their first seat choice - window, aisle or middle as the case may be. There is absolutely no reason to stand in line unless you want an exit row. And that is not guaranteed even if you are at the front of the line, because there will always be preboarders.

So it is a huge waste of time and energy to stand in the A line. You could just as easily be using the time to stock up on food, use the restroom or simply relax and read the paper.

Now the B line is a different matter, as you may find your first choice taken if you are boarding near the end of that group.

C line is also a waste of time, you're virtually guaranteed a middle seat so you might as well not even bother getting up until last call. And you might as well check your luggage since the bin space will be gone.