What I found in my banking and insurance applications is that the models must support complex business situations, be actively used and designed to support/change/control the environment and be easily enhanced by the local support staff.

In every project we developed a local expert had a ‘system' of excel files that the application team was very happy using.   These ‘organized bodies of knowledge' did address the many of the tough application areas but required the ‘expert' to run and where limited in scope.  Many expects had extensive vacation banks because no one else could use their excel systems.  How can you cost justify a maybe costly model if the job is getting one by the current staff?  Once the modeling domain covers several of these excel supported areas no single expert has the individual intuition or experience to support it.  At this point, the issue of sharing knowledge must be addressed.

No matter if it is an Excel system or a complex model, if they are not used routinely by the staff as part of the standard operational process they get out of sync with the current process flow, rates, schedules, user skills, etc.  If the models are only used in special cases or to evaluate what if analysis scenarios, etc. users will have the neither faith nor current skills needed to use them effectively.

It is a fact of business that if a model needs external resources to make enhancements there will come a time when funding will not be available.  Once out of sync with the current processes the model can't be used as a standard process tool and the model fails aside.

Our goal was to leave a process parameter driven operational model in place using the current process data for rates, schedules, etc. used by the front line managers to staff, schedule, etc their domain. 
What are the characteristics of the BSG modeling projects?