The following is just one example of what I mean by the blessings of the internet for the art student: A tutorial clip with Thomas Fluharty by Schoolism, tons more stuff to explore on their site:
Using charcoal: not the most forgiving of media, especially if you have to grown used to command-z/apple-z.
A few times during the duration (???clumsily phrased) of this video tutorial I thought ‘aach, noo?!! He’s ruined it now, should’ve left it as it was’ and then he pulls it off like that…
That’s the point, however, to have the courage to push what you’re doing further but stop before you overwork it.
And as for needing to know traditional media before embarking on the digital? It is certainly useful,but why would it be a one-way-system? If you have started out digitally it can help you once you start taking a stab at using actual materials, and that may improve your digital work in return. In an anti-vicious circle. Why not?
I have heard that you cannot sculpt what you cannot draw – and I would beg to differ here, too.
Sometimes it is useful to build a 3D model or look at one, to be able to draw the physical appearance of something from certain angles. There is no hard and fast rule and barrier, it is like a positive cross-pollination of different styles and disciplines and perspectives.
Maybe leading to new and as of yet unknown fruits of happy labour.
Now go and find out for yourselves!
Blaustift 
Really impressive, someone who has published things in TIME magazine! And as for the sculptures, I am with you, maybe halfway at least. While I think you have to at least know how to draw something (kind of at least) I also think sculptures often can help drawing because you are able to view from ALL the angles…
man sieht auch schön von seinem Video dass man wenig oder einfache Materialen nutzen kann, mit genug Übung kommt wirklich etwas dabei heraus