It is a diagram to illustrate connections between various service elements — people, instruments (both digital and physical), and processes, tailored to particular touchpoints of the customer journey map.
Service blueprints are a good addition to the customer journey map, as they allow reflecting complex scenarios with numerous service-related options. For instance, the goal of buying food in a restaurant can have three different blueprints of ordering online, takeaway or dining at the place. Service blueprints are always to follow business goals to make the product better.
The technique provides the fuller vision of resources and processes, seen and hidden for the customer, involved in achieving the business goal. It reveals weak points, optimization-required areas, as well ass marks cross-department matters and facilitates the determination of responsibility for them.