Optimal word counts

Knowing your market is probably the key, but if you're just writing something to sharpen up later when you have a specific target then you're wasting your time if you put down any more than about 300-400 words. I've found this is a fairly natural length to get your argument sorted and it's easy enough to expand out if you need to.  Plus you don't feel as bad about chopping out a hundred words as you would 300.