The ideas around Structured Log Testing has come out of real world situations of building complex multi-system applications that where hard to test. The methodologies developed work not just for complex systems but for simple cases as well.
The approach has pros and cons like any solution to problems in the software realm. One of the big benefits of the Structured Log Testing is its flexbility. Flexibility on the development and production. On the production side I mean building test scripts and getting robust feedback from end users, making not just the developer but having the potential of dev to end users being part of the testing team.
Along with flexibility is using custom tools that are dynamic and morph with the data you are testing. For example if you are debugging standard message flows that have distinct visual cues if there are problems, tools can take the standard log statements and create testing views that make sense for that application.