One of the key benefits that the PRINCE2 project management methodology brings is the emphasis on consistent improvement and benefits. Documenting benefits is, as Andy Trainer points out in this post, an essential element in achieving buy-in from stakeholders and team members as well. It's not always easy to document benefits — especially if the user doesn't clearly define what the benefit is when asking for the project to be completed. This can be mitigated by utilizing a technique called the “5 Whys method”:
A useful way of helping the Customer or Senior User to identify expected benefits is by using the 5 Whys method of root cause analysis, a technique used in Lean Six Sigma. Asking the Customer what they want (a new product), why (they don't sell this but others do), why (if other people sell it, it must be in demand) why etc. Usually, the Senior User will specify and defend the benefits ““ this will form the basis of the business case. They will be in line with the business's high-level strategic objectives, and any benefits management done as part of programme management where relevant. The inclusion of the end user in the PRINCE2 process is another key to its beauty and popularity.
By using this method, the project manager can successfully complete the benefits review plan, which allows for a clear view of the expected benefits, who is responsible for measuring the success of achieving those benefits, how and when they will be measured, as well as other tolerances, dependencies, and disbenefits (what potential issues or risks the benefits either will or are very likely to bring). Project managers who are able to perform successful benefits management will likewise be able to quickly identify if the work they are completing is in fact within the scope and moving the project closer to the expected benefit. No customer likes receiving a product or service that doesn't satisfy its expected value, and even if a project manager does everything else right, a non-achieved benefit can cause a complete failure within a project.