My students hear me ask this question over and over. I can emphasize the importance of values in drawing and painting enough! Without a range of values, a drawing or painting looks flat, there is no getting around it. You have to get the values right, or else it won’t have depth or dimension.
I set up this still life of black, grey, white, metallic and transparent objects to prove the importance of getting the right values. If the values are correct–and the forms, perspective and proportional relationships are in place–you will have success. This is a very workmanlike study of simple objects, the kind of thing you do in Drawing 101. However, this type of practice will get you a great deal of experience in terms of improving your observation skills and learning to see the importance of the relationship of values.
I wouldn’t dream of starting a big painting without doing an under painting that breaks down the values (not to mention blocking in the composition and getting the drawing correct). It is the structure of the painting. Yet many artists are in such a hurry to get to the color component of painting, they ignore or rush through the most important stage–the values! If you are a representational painter, whether you chose to paint photo realistically or loose and impressionistic, you need to have correct values mapped out in the beginning in order for your painting to have depth and dimension. Drawing matters! Loose does not mean sloppy, practice your drawing skills whenever you get the chance, they will serve you well!