The Diagram Disable Structure is useful during development because you can disable or comment out sections of code. This allows the user to develop sections of code without it affecting the execution of the application. Only the code in the Enabled Subdiaram will execute. You can add more than one section of disabled code or enable a different code section by right clicking on the diagram and changing the settings.
In this snippet there is one section of disabled code and one section of enabled code. You can switch what section of code you wish to enable.
Don't forget about Context (Ctrl+H) and Detailed help when looking at functions that you want to learn more about. The help files are also located online if you want to view the detailed help, but don't have LabVIEW on that computer. Here is the help file for Diagram Disable Structures, but you can also search ni.com to pull up other HTML help files.