For a single touchpoint, understand the user, task, and channel, and optimize the steps, data, content, and processes needed to support the touchpoint.
Why to use? A touchpoint map helps teams optimize a touchpoint's experience for the user as well as improve its effectiveness for the organization.
When to use? Map touchpoints before you design interfaces. Touchpoint maps breaks user stories into discrete elements that support backlog grooming and sprint planning.
The following resources provide more information about using this method.
Collaborative Product Design by Austin Govella
Chapter six provides detail on variations and alternatives for using this method.