Importance of Level Design

I've just launched a level design course featuring Knytt Stories thanks to it's excellent and easy level editor tool (which, rather than be frustratingly difficult to handle, will allow people to quickly throw together a level) (And this part of the course is about basic understanding of level design as well as abstract theoretical tools, rather than managing 3D-worlds). I was positively surprised, even though I've already held this course once, to what extent level design is a brilliant way to let people experiment with their design ideas or ambitions. A reoccurring problem with the design courses are usually the amount of design work that there simply isn't time enough to prototype, but small, relatively flexible editors such as the one in Knytt Stories, are capable of a broad range of design ideas. Knytt Stories, especially, and this is what's making it rather unique, is an extremely powerful tool for trying out simple ideas of how to set a mood, an environment or depicting an underlying tone in a game (which is a crucial skill usually amiss in commercial titles). The only other example I've stumbled upon would be the Age of Wonders-games for which I've done an unhealthy amount of scenario editing.
They both (age-of-wonders and knytt) are simple enough to use and support the combining of tilesets to create new, unexplored expressions, why both allow you to quickly try out a visual style and attempt to recreate a mood.

To summarize, I don't think level design can be used to develop and test all different game design skills (there are plenty), but by carefully picking editors and outlining what they can establish or depict quickly and effectively, I believe design practices can be made more beneficial and practical through the use of level design exercises.