The cylinder is usually the shape we use to visually describe the main parts of a figure or character after drawing the gesture. It's probably the most important shape to know how to draw correctly, after the box, because the box is what we use to contain our cylinder.
The head, torso, arms and legs and fingers can all be simplified using this basic shape, which is deceptively hard to draw correctly because of perspective.
But luckily we don't really need to draw perfect cylinders in perspective, just practising to draw them perfectly is enough. In the end, if it looks right, it's right. If something looks odd, then we need to be able to know how to check our basic construction and design frame using the skills we've developed with practice.