Contrasts are an important feature of any drawing. With too little contrast the image can look flat and dull and similarly with high contrast and no mid-tones will lead to lack of depth.
You may have seen many drawings with gray or dark backgrounds and these types of drawings can be an excellent way to get into drawing if you are at a beginner or intermediate level. If you look at a drawing with a distinct white background, the drawing may not be as forgiving as say a gray background. This is due to contrast and a pure white background means you need to do a good job of the actual drawing as opposed to muted background.
In essence, a dark background for a drawing is helpful for you to focus on developing your techniques and the drawing will appear better than the same drawing on a pure white background.
In this drawing, we draw an apple set against a dark background but at the same time we play with the background effects to add an interesting twist to the final drawing.