I'll give you the answer one of my college professors gave to students who asked how long their term papers should be: As long as it needs to be.
(Helpful, right?) But really, your blog posts are no different. They should be as long as they need to be to serve their purpose -- whether that's thought leadership, driving leads, explaining a new concept, whatever.
Can your blog post serve its purpose in 200 words? Cool. Stop writing. You're done. If you need more words ... cool. Keep writing. You're not done.
When you're done talking about the subject at hand, and you've edited your content to be as useful and economic as it can be, your blog post is exactly as long as it should be. This could mean you have a blog post that's 2,000+ words (like this one here) or one that's less than 100 words (like this one here). (Hint: They both performed well.)
1) Don't be scared of a long blog post ... or a short one. There's no word count police.
2) Brevity is the soul of wit. If you can say something more succinctly, you should. No one likes to read, anyway ;-)
3) If you're new to blogging and the idea of having no word count guidelines stresses you out (which is certainly fair), take a look at what other business blogs you admire are doing. Just don't feel constrained by that word count!
And a Parting Tip
It's natural to think that a really long blog post is hard to write and short posts are way easier. I'd say the opposite is true.
In a short post, every word choice you make actually matters more. If the idea of writing, say, 800 words (or 8,000) freaks you out, take some comfort in knowing that the word count actually provides you with a little cushion to be less choosy with your words.
How much do you think about blog post word count when writing?