Validate only
When you enable the Validation Only; Do not change Database button, the database is not updated. Data is checked and reports all errors/warnings. Errors that could only be found if the data was written to the database are not reported. For example, if you add a Trading Partner and then add the same Trading Partner later in the validation run, that error is not caught in a Validation Only run, as the database was not updated.
Note: It is recommended to run your XML using the Validation Only option first to find syntax and other foreign key validation errors.