In reply to Adrian Lyons.

Some plugins add extra options/settings hat enhance WordPress settings, like those on the Writing, Reading and Permalinks options pages. In many cases the user will not first think of what plugin, but what kind of thing to change or adjust.

So plugins must be able to hook into any screen.

Some plugins provide a link to it’s own settings page on the plugin screen. This may be made kind of mandatory, in case there is one.