As well as this, it's clear that the more blog posts you put up there, the greater the odds that you'll draw traffic via "long tail" keyword searches. While each of your posts may only bring in a few hits every now and then on average, if you have lots of them up then they will still add up to a respectable number.
You also find that if you frequently update your blog you are more likely to get and keep regular readers. Just as you are in the habit of writing new posts, they get into the habit of returning to see what you've come up with. (They tend to comment more often, too. And which blogger doesn't want those? They are proof that you're making an impact, after all.)
But you do have to keep up the same posting rate to retain those regulars. If you have a break for a couple of weeks you may find that many of them have just given up and don't come back even when you resume at the same pace later on. So you can feel a great deal of pressure not to slow down for fear of this happening.
If you have a money making blog which is successful, then obviously the more frequently you post, the more profitable it is. That's another reason to keep up a cracking pace.
These forces, particularly in combination, can ultimately be a bad thing for blog quality. If they're your main reasons for posting, as opposed to just wanting to share unique and interesting information, then you're "putting the cart before the horse".
That's why it is better to not worry too much about how often you update your blog. You should really only write a post when you've got something interesting and thoughtful to say. (Of course if you only feel inspired once every three months, then maybe blogging isn't for you. At that pace it will take you years to draw any traffic!)
But if you can add good content weekly that will still be worth it. And you can ensure that those ideas will come quicker if you are constantly absorbing information. So, you should always be reading other blogs in your niche. Doing this is a nice break from writing, anyway.