Hi Dan,
thanks for an interesting post!
Just to set the scene, I've been a modeller for over thirty years. Over that time, I've had an opportunity to observe how I and others use models to achieve the outcomes they want.
Also, these days I work mainly in the enterprise modelling space.
In addition, I'm developing various Add-Ins to leverage off EA's functionality to provide a large-scale modelling environment. So, I too am interested in the various use cases!
People's needs from modelling is quite different depending on what their roles are. For example, if you are the sole or primary user for a particular model your viewpoint will differ from those who need to use a model to aggregate information from various sources to get a combined viewpoint unobtainable from any other method.
Also, I've come to realize that if you have multiple viewers (such as, for example, in an Enterprise environment) it is very advantageous if you can provide multiple methods to access the same facts contained within the model. I call this concept - "
Same semantics, different syntax". Thus, as you point out below, the diagrams and the workbook might contain exactly the same information.
I'll cast the rest of my response in the light of the current project I'm working on for a customer which utilised a number of the Add-Ins I'm developing
I really hate it when people suggest that I have a problem I should not have rather than helping me solve it. Now, I'm about to do that to you. Sorry. I mean no disrespect and I am only interested in the use case.
So, our problem is that a significant portion of the enterprise's administrative functionality is to be outsourced. However, the processing that is to be outsourced, needs input data from the existing systems and will return processed data back to the existing systems. We need to know where the data currently is, and what inter-linkages there are - especially between database and the processes which move the data between them. Because of the nature of the enterprise, there are a large number of locally maintained, bespoke applications - many of which use an ORM and common data layer (with code generator). In addition, there are a number of data synchronization and movement processes using MS SSIS etc MS Access databases also figure significantly as well as server based ones - both Oracle and MS SQL Server). Certainly, a typically polyglot environment. And did I mention the Visio diagrams and Excel Workbooks?

So the primary problem in this case is to obtain an integrated view of where everything is and how it is connected - not to mention gettitng consistency (my
signature word - as you know) between these various holdings. These systems and documents have been developed over a number of years by various people, many of whom are no longer around.
I use the diagrams as input mechanisms. The only diagrams I have are the ones I used to figure out what I intend to do. When it comes time to change functionality, the first thing I do is look at and change the diagrams. If the diagrams are not useful for this purpose, I do not create them.
Most enterprises (in the enterprise modelling space) don't have enough diagrams of the stuff they need to manipulate to start with the diagrams! That, indeed, is my first job - to create the integrated model and associated diagrams to allow the developers to trace the linkages "from end-to-end". This is being done using a number of "harvesting" Add-Ins. data and Information Harvesting is a concept I'm promoting in relation to large scale, organizational modelling (at enterprise and near-enterprise levels) to collect, collate, and make consistent the information located in various parts of the enterprise. This is typically held in databases, development tools, spreadsheets, documents of various types.
As we increase the number of sources and links, the management of diagrams showing what is related to what becomes asymptotic. One Add-In scans the input provided by EA from reverse engineering DBs and creates
Creation, Insert, Update, Deletion etc dependencies between the various tables, views, procedures, functions etc. This allows the developers to "see": "this procedure uses these views and these tables and these functions and calls these procedures" - you get the picture.
Another Add-In scans the project files of the ORM Generator and creates a model in EA of the artifacts used therein and how some of those artifacts link to the previously created DB artifacts. Yet another Add-In reads the MS SSIS project files and does the same.
[End of part 1]