Why?
Because I have just had to go back and edit another handful of posts where I had stupidly forgotten to assign them a category.
So?
Wordpress used to have the category selection box towards to the top of the page, above the fold on the post creation page. It currently resides below the fold. There are plugins to bodge the position, but I don’t like fiddling with key files too much unless really necessary. WordPress 2.7 will apparently allow the various panels to be moved around. This will mean I can see the category box before I hit the publish button, meaning less posts will hopefully find themselves mistakenly in the default ‘Personal‘ category.
Ah, so your laziness/forgetfulness is the key problem?
Yes 🙂