A time consuming task for architects is the evaluation of the project's intended occupancy and its impact on egress from a building. It is possible to improve this process considerably with Revit by reporting data in Room schedules. However simply reporting this same information in a room tag isn't so trivial.
The fundamental problem is that we can not display data that we calculate inside the project in a tag yet. A tag family can not use the area value in an equation because it doesn't exist until you are in a project.
This FILE is an example of a strategy that reduces some of the drudgery of looking up data and having the numbers "crunched" but leaves us with manual data entry to get the information in tags so it can be display meaningfully in plan views as well as listed in a schedule. I did the work in this example but the inspiration goes to WLC Architects, where Scott Davis used to work. It is an imperfect example/solution but should serve as inspiration for your own approach to this issue.
Some of my thoughts about how this might change in Revit:
We need a way to tell Revit that a tag will use a project value, like area, once it is inserted and an object is tagged. A placeholder for AREA that will assume the true value when you tag a space but in the family itself substitutes a temporary value so the formula will "work".
Alternatively we need a system family tag type that can combine instance data like Area with other shared parameters to display calculations.
A third concept might be schedules that actually behave like tags and allow freeform placement of parameters and linework to look like a tag.
Yet another is to allow us to map one parameter to another within a project. Essentially allowing what we have done in these schedules manually to be done automatically, ala Excel...Cell A1 is equal to Cell J4.
In terms of value delivered, this sort of evaluation/calculation is a process that all firms go through to some extent. Evaluating occupied spaces and demonstrating how the design meets the code. This is a business problem Revit needs to help us resolve. Giving us greater ability to decide where and how information will be displayed is very important.
The bottom line is we need a way to display calculated data in tags.