The preflight process will check the following items:
- Missing linked items (images, ...)
- Missing fonts
- Image resolutions based on the alternate layout
- Page sizes
- Alternate layout names
- Alternate layout page counts
- Size of scrollable contents
- Multistates (to see if they don't exceed the page size)
- Image Sequences (source folder, does it contain image files, the correct file format, image sizes, ...)
- Buttons (unsupported events, …)
Depending on the severity, the preflight will generate either a warning (and allow you to continue), or generate an error (in which case you cannot continue until the problem is fixed).
In the plug-in preferences, you can select whether warnings are displayed when doing a preview, or when sharing and exporting. If you uncheck both, then Preflight will only bug you when it encounters an error and is unable to continue.