The usage section explains how to create framesets, but does not discuss all aspects of appropriate usage. This section will focus on questions such as providing alternative content, handling outgoing links, and making the decision to use frames or not.
One of the more common reasons to use frames is "because it's cool", or "because I can." This should never be a consideration for a serious site - a personal or "for fun" site can of course do whatever it wants. The main advantage of frames is the ability to display multiple documents at once. So the question can be rephrased to "What kind of documents do I want to see displayed at once?" or "How would my readers benefit from seeing two documents at once?". If there is no good answer to this question, then the site does not need frames.
An accessible site will always have a "noframes" version of the site available, for viewers who do not have frames, or prefer a traditional version. To allow users of browsers without a "frames off" button to use the noframes version, include a link to the noframes section. Similarly, you can include a link to the framed version in the noframes version, which could be handy if the user came in through a bookmark.
The important decision is: does the starting page have frames or not? In both cases, links can be provided to the "other" version, so users always have a choice. There are arguments for both choices:
It is most unfortunate that frames are "transparently backwards compatible" (as one "cool" author puts it) - which means you don't see anything if your browser does not support frames. The author has to provide alternative content manually, using the NOFRAMES element. Usually, this needs only be done for the frameset documents; if the other documents do not rely too heavily on frames being used, they can still be used by traditional links and navigational elements.
One problem is that with the common "table of contents" frames application, the content documents no longer have navigational links. Although the user can still read them, he has to navigate through them by using "Back" every time and choosing the next one from the menu provided in the noframes section of the main page. This is rather tiresome.
There is a solution: use server-side includes, or use a preprocessor to generate multiple HTML documents from one source. This way, the toolbar can be included at the bottom of content documents if they are read "standalone", and left out if the content document is loaded through a frame.
Always make sure all outgoing links remove your framesets. It is very frustrating for a reader when he can't "get out" of the frames at your site when he has long since left. The author of the other site might also get upset, because it looks like his content is on your site. This technique is used by some less honorable people to pretend the other material is theirs, and so it is frowned upon.