Are you impressed by artists who are able to achieve high levels of realism in their work and wish you could also get to that point, someday? Interested in bringing realistic form and three-dimensionality to your drawings so that they can really pop out? Have you gained some confidence creating line sketches, and are ready to start adding realistic light and shading effects?
Even though I consider myself much more of a sketcher and a painter than a realistic drawer per se, I think it’s essential to make time for these kinds of studies. I also think that it’s important for aspiring artists to devote time to achieving believable drawings/paintings because this is what’s going to lead them to develop great observational skills and grasp fundamental art topics such as proportion, value, perspective, form, etc.