Oh, line of action. How rarely do I use thee. I really should, though. It's a good tool for conveying a realistic sense of movement, which I see here.

The first one on the left is really great. The position of her hips compensates the backwards leaning of her upper torso. I'm also impressed by that lying pose in the upper right corner.

Lines help, yes.
These are used in lots of animations and an amazing tool.