Why is there space in between the keyboard and the unit itself?

If you look at the side with the little LED light and black sensor, you can see a little space, a little line in between the keyboard and the bottom unit itself. The other edges don't budge when I push down on them. But, the right edge, with the LED light and sensor gives way just a tiny bit.

Is this normal. Is there more space on a certain side of your mac? Is this so you can open it when you unscrew the screws? I'm trying to make sure this isn't affecting the stability of my screen. Would the little crack affect how sturdy my screen is?

Just trying to figure out why there is more space on this side than the other?

Also, i'm not talking about the obvious space that is supposed to be between the lid and the bottom part of the computer. i'm talking about the little crack in between the keyboard and the bottom of the unit.

this last picture you can see the little crack

Thanks!