As a tech writer, I have a bias towards programs that make it easier for me to communicate graphically, especially when a step-by-step process is involved. Napkin 1.5 helps enormously by letting me take an image—whether a photo or screen capture—and quickly annotate it in a way that looks professional and can be edited later.
This is a niche product that, for the right person or company, will save inordinate amounts of time, and it requires only a few minutes to master. That compares favorably to using, say, Pages or Keynote and exporting the results in a fashion you can use. Napkin’s interface is intentionally limited and simplified. There are few tools and little elaboration. But simplicity is a benefit when the right choices are made.