Ultimately, the purpose of your weblog is whatever you want it to be: most weblogs achieve several purposes simultaneously. The mix will depend on your circumstances and your personality. Still, it is helpful to take an inventory of your five favorite weblogs and ask yourself what each of them is trying to do.
Source: The Weblog Handbook: Practical Advice on Creating and Maintaining Your Blog, Pages: 65
Contributed by: ~C4Chaos