This option lets you disable the Warnings and Errors dialog box that appears during the import process. The Show Warning Manager option is active by default.
What is the difference between an Error and a Warning?
The Maya FBX plug-in uses errors and warnings to alert you of conversions and potential problems during the import process.
When something unexpected occurs during the conversion, the plug-in reports an error. This error occurs because the Maya FBX plug-in encounters an unknown behavior and the conversion is going to produce an unexpected result.
When the Maya FBX plug-in must apply a conversion to the source data for it to be in a format that the destination application can read, a warning is reported. This warning is not the indication of a problem, but instead exists to provide a report of conversions that have been applied to the incoming data.