For practical usage, keywords are great when you need to express some form of information about a document that might not otherwise appear in the document. An example of this might be a section of narrative that discusses a character, but never actually mentions that character by name. Throw in the character’s keyword into the meta-data and you’ll never have to worry about losing the piece.
In the post that you linked to, I was referring to the use of keywords as a way of enhancing workflow. Status and Labels allow you two axis of information for any document, but there are definitely times when a third axis is necessary, and where it must remain independent from the other two axis. A simple example would be: You are using Labels to define document types. You have a green colour assigned to character sheets. The status indicates that this particular character sheet needs to be fleshed out a bit more. Perhaps you just wrote a stub in a blaze of inspiration, and tagged it with “Expand” so that you’d know to come back to it in the future. Enter the third axis, you are taking a small vacation into the country by train, and cannot bring your computer with you. So you want to print out a selection of documents you’ve written so you can work on them with your pen and paper while on the train. You can create a keyword called “Print Me”, and drop it in under “Work Flow” in the Keywords HUD. Assign the “Print Me” keyword to all documents you wish to take with you. Then on the night before you leave, you can do a quick “Print Me” filter search, and independent of the other two axis of information, get a quick list of every document you want printed. No doubt, you can think of many other situations where this might be useful. There are times when you are doing certain types of large scale edits to your book – perhaps doing science checks on all dodgy statements. If you were diligent in marking down every section with scientific declarations, you could filter by “Check Science,” and work down the list. This is the type of thing you wouldn’t want to create a full status for, because very likely it would conflict with other status indications such as “Rough draft.”
Now, the way I work, is using Annotations as I write to mark things down. I’d rather not bother with keywords until my flow of thought is complete. Pressing Cmd-Shift-A, tapping out a quick reminder, and then dropping straight back into the narrative is wonderful for just this sort of quick note to yourself. I have a system of short identifiers that I use. So an annotation on science might look like [SCI : Check to see if it is physically possible to fall from this height without losing consciousness ], and then keep typing. Later, once I’ve completed a batch of writing, I can do a quick regular search for “SCI :” and every document that has been tagged with these types of notes will show up. Select them all in the Binder, open the Keywords HUD, and drop the keyword onto the selected group. I now no longer have to worry about accidentally losing a note in the text itself. Further, if I know I have hundreds of such notes, I also have a modifier code system that I use. I can search for “!SCI :” and that will return everything that I considered to be very important to fix. An “Important” keyword can be added to these – another third axis.
These are all just ideas. There are certainly many more ways that Keywords can be exploited, including much more simple ones. The key thing is that, if you are diligent in using them, they will become a repository of quick information sources that you can trust above regular quick searches.
In the end, it is all a matter of how you work though. Some people will never find a need for a third or even fourth axis of information. Labels and Status will be enough, and regular quick searches will accomplish the rest. They are there if you need them, easily ignored if you never do. And I suspect, given some hints dropped by Keith, they will be even more easily ignored in B3.