I think it's really, really great that people contribute documentation and third-party products to Plone and publish them on plone.org. However, as the reviewer of a lot of the submissions, I have one complaint:
Selecting every conceivable category, audience or section makes your content harder to find, not easier.
80% of the items I review have selected four or five audiences (Oh, you know, this is relevant to site administrators, developers, advanced developers and integrators, customisers, maybe), or two or three product categories (hey, there's code here, so let's call it a code example, and also it could go into the misc category, and really, it's a service so let's put it there too).
Unfortunately, that just makes the categories less useful to everyone.
This is why we have reviewers, but reviewers forget to check the categories (or they make the same mistake) and we end up with cruft. We could change these to a single-select field, but there are cases where we need multiple categories. Perhaps we could introduce a validator that means only reviewers can select more than one category, but this is somewhat clunky.
So please - apply some critical judgement. The categories are there to make it easier to browse the content, as the listings are grouped by them. If every grouping has every item, then we may as well just not have categories.