The CPU usage should not go up unless the subVI is running, and it didn't go up when I tested it. Even if the subVI is running, it should probably not go up much unless you put 0 in the wait or delete the wait.
I'm not sure what you're seeing, but I'm not seeing it. Could you post a screenshot of this, or list exact steps for how to recreate it?
To learn more about LabVIEW, I suggest you try searching this site and google for LabVIEW tutorials.
Here and
here are a couple you can start with. You can also contact your local NI office and join one of their courses.
In addition, I suggest you read
the LabVIEW style guide and the LabVIEW user manual (Help>>Search the LabVIEW Bookshelf). The user manual also includes a chapter about events. You can also try searching the site for specific tutorials about event handling.
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