Although drawing is a personal process and there is no right or wrong way as long as you’re happy with what you see appearing on the paper, “sketching” and “drawing” are at different positions on the continuous loop of drawing methods.
Sketches are usually made to work out possibilities and to find the best composition. Sketching is about capturing an essence instead of lingering over details. It’s an excellent way to keep drawing skills sharp too.
Because it’s done quickly, you have to find the most important parts of a scene first and that’s good observational practice. You have to simplify as you sketch, which exercises your ability to see qualities like value, form, line, and texture. And while your brain is busy looking and judging, the muscles in your hand are learning how to handle a pencil like it’s an extension of your fingers.
Drawing is perhaps more thoughtful. The process can be slower and more careful. You get to linger over the qualities of the scene, create all the detail you want to, and refine the look of the piece until it says all you want it to say.
And Everything In Between
There is a huge range of possibility between sketching and drawing as they mix and overlap and dance around together too, and my definitions are only my opinion. So, draw what you want to however you want to and maybe not thinking about it too much is the best way to draw of all.