Categorisation is a GoodThing. It means that pages have something at least semi-stable to hold on to instead of drifting off into the void and being forever lost. This, in itself, leads to more problems such as the same content appearing under different names as people forget it has already been written elsewhere.
Hence, when writing a new page, try to assign it a category or two.
If you are unfamiliar with the categories that are currently available, a search on CategoryCategory will return a list of them. In fact, now we have personal links, putting "&search=CategoryCategory:FindCategory" in your preferences page will add a quick link to the category listing.
Side note: CategoryRandom and CategoryUncategorisable should be, if possible, reserved for things which truly are random or uncategorisable, not just things that didn't seem to fit elsewhere.
Don't forget that you can create your own categories if you feel it is something that will be relevant.
If all that fails, CategoryPending is the place for you. It is basically a plea for help for other ToothyWikizens to assign the page to a real category.