You draw the object (usually a figure or a thing, but it’s only a guess), and then the sketch is drawn on the paper by a different person (often the same person you’re working with).
In the first half of the twentieth century, when people were beginning to sketch themselves in the mirror, the person who sketched the object would sometimes write the drawing so that other people could see it, then, after the drawing was finished, the artist would look at it in the mirror to see whether or not it looked like the sketch. At the very same time, many artists would sketch the shape of the object and the general shape of it, or, if they couldn’t get around that problem, the object itself, so that any sketching could be seen as something of the object itself.
But the work of drawing on paper didn’t necessarily mean taking the time to try to draw the shape of an object. Many artists didn’t even begin drawing (or they thought of drawing as an exercise for the brain, not a real artistic practice) until they could figure out how to draw in a particular way that made the object seem drawn.
But many of the artists who did actually start drawing (or who were already sketching) tended to do it in a way that made the object seem like it was physically drawn, if only because they were drawing it as if it were physically drawn. This could make the object seem more real even if it wasn’t.
The “spare” or “blank” notebook is often considered by those artists who did start drawing as proof of their practice, whereas the “real” drawing is still just a sketch. The “blank” notebook doesn’t always make it possible to tell which was which, but we can make educated guesses.
You don’t need to spend a lot of extra time getting into the habit of sketching before you’ll go to the trouble to do it properly.
It is not necessary to spend a lot of time to do your sketching.
For those artists who do decide to spend a lot of time on sketching, there are a number of reasons for doing so. There are probably a number of different things you could be sketching, but the most common reasons are: to figure out the idea, to find the ideal proportions, to study how an object is represented or how it’s presented, to try to figure out a good way to express the idea, to find the style of the object, etc.