I tend to think of weblogs in functional terms, as well as in structural terms (where weblogs correspond to sections on my site). As was mentioned earlier, it’s a good idea to do some good analysis of the content on your site. You might find that you can use one weblog to control multiple sections of your site.
For example, if you go to http://hahndentalclinic.com/meet-the-doctors/ and http://hahndentalclinic.com/meet-the-team/, you’ll see that those are two separate sections of the site. However, the content of both sections is coming from the same weblog.
When the site’s administrator adds a new staff member, they select which category that staff member belongs to—they’re either a “Doctor” or a “Team Member”. The templates for the two pages are then coded to pull in the correct content, based on the category.
Another example of this might be an event calendar. Say you’ve got a website that displays information for multiple departments, and each one of those has their own event calendar. Rather than create separate weblogs for each department’s calendar, I’d create a single event calendar weblog, and then organize the events using categories, where each category corresponds to a department.
Then, as with the site above, I would set up each department’s event calendar template to pull just the info from its corresponding category of event calendar entries. (This assumes that each event, regardless of department, contains the exact same info.)
In the above examples, I’m thinking of weblogs in terms of their function—what they do—and not just in terms of their location—where they reside on my website’s site map.