For services in general—but especially for digital services—separation of duties is a crucial principle. Butchers do not inspect their own meat.
Someone who is good at a certain type of work does not necessarily excel at complementary tasks. For example, a project manager may be very skilled at monitoring his budget, but the finance department is better at rendering financial accounts in accordance with the controller's requirements. Separation of duties.
A functional administrator may be very good at (helping to) record the user's information needs, but skilled programming requires a completely different skill set – not to mention the day-to-day management of the application. Separation of duties.
A designer may be able to produce a well-structured form, but the accessibility expert assesses whether it is also suitable for people with disabilities. Separation of duties.
Another example: someone who is busy coordinating and handling operational matters often has more than enough on their plate. You don't make that person responsible for improving their routines at the same time. In practice, they will never get around to it. Quality improvement requires a pair of fresh eyes that can see the big picture, analyze where improvements can be made, and help those carrying out the work to develop better routines. Separation of duties - between process managers and coordinators.
And anyone who makes a mistake in a design will not easily notice the same mistake when implementing it – which is why testing is a real profession. All in all, there are more than enough reasons to make a clear distinction between specifying a solution and implementing that solution: separation of duties.
When you apply separation of functions, you create handovers between the separate task areas: the functional manager delivers the functional design, and then the technical manager gets to work translating it into a technical design for implementation. Such a handover gives you the opportunity to exercise control over the overall quality: will the entire chain ultimately deliver what was expected at the outset?
In a field where we can no longer afford to make too many mistakes — for the simple reason that others are too dependent on us — control has become inevitable. Separation of duties, together with standardization, is a powerful tool for this.
