There are many ways to measure the usefulness and benefit of simulation projects.  One of the overlooked areas is training.  Training simulations tend to give a lot of benefit for the effort required.  Usually these models are used over long periods of time so the cost is spread over a long time horizon.  There are a number of different ways you can use simulation as a training tool.  Here are some past ways that I have worked on that had training components:

1. Sequence of Crane Operations - A large airplane manufacturer had operators who operated multiple cranes in concert to build up the major pieces of an airplane.  Often two cranes had to work in concert and carry a large part across many bays that would halt work in those bays during the slow, arduous move.  A simulation model was created to train operators on the best sequence for the infinite number of potential timing decisions they would have to make.  The model was run with different rules to minimize the time to assemble the plane based on the sequence of operations.  As the operator interacted with the model to instruct the move he/she wanted to see next, the model would provide feedback that the model agreed with the choice or that it would have made a different move.  This was a really cool way to use the model as a repository of best practices because the model could be updated to reflect the better decisions that real world experienced operators would naturally choose.
2. Time Based Resource Allocation - An aluminum can manufacturer uses molten aluminum to create ingots that are rolled and formed into cans.  The molten aluminum is made up of a mixture melted aluminum ore and shredded aluminum cans that were collected from the public.  Each of these two sources is melted at independent locations and transported to the furnace that feeds the ingot molding process.  The transportation mechanism for the melted ore and melted shredded cans is a crucible that holds about 1500 pounds of aluminum.  Once aluminum is poured into a crucible, it must be used within 6 hours or it will harden and ruin the crucible.  The chemistry required by the ingot dictates that a certain percentage of the aluminum needs to be pure ore and some of the ingot can be formed from melted “reclaimed” cans.  A Metal Caller has the job of deciding which crucibles of melted aluminum gets used on which ingot.  They also have to tell the aluminum sources when they need more aluminum and how much to send.  A simulation model was used to train the metal caller to maximize throughput and minimize the number of crucibles that were “frozen” since they were not used in the 6 hour window.  This type of feedback helped train new metal callers or assisted people unfamiliar with the process if the normal metal caller was away or on vacation.
3. New Employee Training - We have built many models that were used initially to make a traaditional capital decision about throughput or manpower.  After the project, these models get repurposed as introductory tools that help new employees visualize a large process or understand how a system should react to various conditions as they arise.  This comes back to the communication value of models and the power of getting everyone on the same page within a particular process.
4. Operator Instructions - For more detailed models that include the steps of an assembly process, simulations can be used to create visual work instructions for an operator.  These instructions can be used as part of a formal training session at a new facility or available at an operator workstation for a refresher on operations that are not used that often.