Imagine that you have an InfoPath form that submits to DBXL. There will be instances that the value entered for a specific field doesn't match the data type stored in the database - thus results in shredding errors.
When errors occur during shredding, the document is still saved in DBXL, but the associated record in the SQL database will not be created. It is possible that a numeric field has an invalid value, or blank. These can be handled by adding a condition on the database mapping to store NULL for these cases or add validation in the InfoPath form. For numeric fields, you can append [string(number(.))!='NaN'] to the field xpath in the DBXL Admin tool database mapping.
For more information about conditional shredding in DBXL, please see this document.