Focal length is one of the most important attributes of the lens. It is just a measure of the ability of the lens to magnify a scene.

The focal length is a measure which indicates a physical distance (depends on the lens type). The distance defines the optical power of the lens and affects how strongly the light is bent.  Less  distance (or focal length) means more optical power and more bending.

For a thick lens, the optical path length of the light is more, than for a thin lens, thus, the bending of light will be more in case of a thicker lens.

Both type of lenses , namely less focal length once and more focal length ones, are used in the industry in various applications like camera, spectacles etc.