Collections of short stories and novellas are among my favorite things to work on, and I plan to continue production and publication of such works simultaneously as I make my way through the various novels and ideas for novels sitting on my desktop.
Short stories and novellas are a great way to introduce someone to your work, your style, your way of thinking about things. I know personally that when first picking up a new author, especially when the author in question is relatively unknown, I don't like being faced with the prospect of four hundred pages. Rather, one hundred or two hundred pages gives the reader a taste, an idea of whether or not the author is someone they wish to keep reading.
I presently have one short story collection and one novella in publication, with two other novellas in the waiting.