There's some anecdote about art where a pottery teacher allowed the students to either be graded by how many pots they created or how good the best pot was. The students who decided to be graded by how many pots they created ended up making the better pots than the ones who focused on making just a few good ones.
Not sure if that's a true story or just an urban legend, but there's definitely something to be said about the value of just doing. As a craftsman, it's not about building the Taj Mahal in the first go, it's about learning flow and learning process. An important part of process is rounding off a project to completion -- getting a sense of when you've completed what you've set out to do.
New Media is weird in that your tool set evolves at the pace at which tech evolves, so you have to round off in new ways over and over.
Sketching definitely helps with that. You get to test new ideas and learn new approaches. I dunno, it's like the difference between learning a language from a book and just getting drunk with the locals and just doing your best to keep up.
Anyhow, I just finished 30 days of Unity sketches. You can download off of Github here. Here are a few screens of some of my favorite sketches:
And here's a gif from the last batch of 30 sketches, using Processing. That Github repo is here.