Schematron is a powerful language, and one of the reasons is because it allows the schema developers to define there own custom messages. The messages can also include hints to help the user correct the problem, but this operation must be performed manually. Correcting the problem manually is inefficient and can result in additional problems.
The SQF language allows you to define actions that will automatically correct the problem reported by Schematron assertions. This will save you time and money, and will help to avoid the potential for generating other problems.