I wrote the following (April 2012) in a reply to a thread at RevitForum.org. It is one example of how a user keynote can be applied effectively to reuse instructions and avoid stating them differently in different places, as is easy to do with regular text elements.
Imagine a data receptacle plan. The data receptacles are essentially all the same (lets pretend they are all 2 drops) except for where they are installed. Some are mounted in a wall, some in a cabinet at a sales desk, some in a kiosk (free standing display), some are available for visitors to use and others are not. As far as a schedule to summarize them, then purchasing and installing them is concerned the faceplates and back boxes are potentially identical. To apply a keynote to define how they are different in use we'd have to consider separate families or separate types so we could get different keynote values.
If we create four or five unique keynote entries we can apply them to the data outlet according to their use as User Keynotes. The keynote legend would display the information for each condition on the sheet and/or in the master keynote legend. The same information could be displayed using a tag showing a custom instance parameter but not summarized in a list on the side of the sheet as easily. Nor could we avoid different values being entered by different people.
An example User Keynote might be:
"Kiosk mounted data receptacles are to be mounted at 12" above counter surface. Provide one extra run of CAT 6 cable without terminations, for future expansion."
The same device could also have a User Keynote that says:
"Data faceplate color selection must be coordinated with interior design final material and color selections with owner."
In the plan view we'd see one device and two keynote tags with different numbers adjacent to each other. If I needed to do the same thing for other receptacles I'd have to create new types every time I needed a keynote to say something even slightly different.
Keynotes as a practice is derived from the desire to reduce clutter on the sheet and reduce the chance of writing instructions differently on different sheets. Using types to control the information is still risky because we could type different information in different types and in different families. If we are going to supply instance parameter values routinely we run the risk of similar mistakes while trying to be consistent. Since User Keynotes are pulled from the same source, as long as we all click on the same keynote the information will be the same everywhere.