travelin_cat - 2:57 pm on Sep 18, 2012 (gmt 0)
Categories are very useful for some plug-ins/extensions. As an example, many slideshow extensions allow you to show images from certain categories. So if you are selling electronic goods, you can set up categories for articles on cameras, video cameras, televisions, VCR etc. and then choose to only show articles from that category in certain extensions.
Also, it's easy to categorize articles for various other uses. They are by no means necessary, but they can be very helpful in many circumstances. Sections used to be a way to further categorize articles, but apparently it was rarely used. I know I never used them.
You do have to choose a category, but as you pointed out, just use "uncategorized".
As you have noticed, Joomla can be very powerful which at the same time can create confusion.
There is a tremendous amount of documentation at joomla.org and I have found answers for every question I have ever had on their forums.
Finally, you are in no way using a dying CMS, Joomla is second to only Wordpress in installed websites followed by Drupal.