We have this great functionality of calcualted values in schedules, but those values never leave the schedule. This means that any calculated values can't be used to filter elements in view or automate any other process in the model.
There are the obvious solutions of using Dynamo or the API, but being able to create a calculated schedule value using a shared parameter would solve a lot of problems associated with having to either push data in and out of Revit or develop Dynamo graphs for specific project uses.
The other solution is to build all of these calcualtions into the family, which I've done many times before however we often don't need these calcualtions across our entire content library and it can make some of the simplest families incredibly complex or sometimes there are one off specific solutions for projects that can be cleanly handled within calculated values rather than needing to rebuild the entire family. Having the ability to drive everything from the schedule means we could haves these schedule templates stored in "shopping cart" Revit models and copied and pasted in.
Having this functionality could potentially give Revit a lot more traction in the engineering space as end users could easily recreate their calculation spreadsheets as schedules in a model and have that data push back to the shared parameters contained in the elements themselves. There is quite a difference in learning curve between creating calculated values in a schedule and creating a family with the calculations built in.