The Jet Engine is synonymous with Microsoft tools such as Access, Excel ( http://www.microsoft.com/office) or when developing with DAO (Data Access Objects), ( http://www.microsoft.com/data). If your application falls into any of those categories, it is recommended that +jetfix is selected.
This option will map Microsoft Jet data types to compatible SQL Types ready for ODBC and data access. For example, the MSAccess Data Type `Money` will be converted to Float or Decimal. This is because not all databases support this type.
For more details on how data-types are mapped, please refer to http://www.openlinksw.com/info/docs/uda50/lite/appendix.html