SqlFunction attributes members DataAccess and SystemDataAccess

If you have looked into using the SqlFunction attribute, you may have seen that there are members DataAccess and SystemDataAccess.  What's the difference in the two, afterall they sound so similar?  The DataAccess member is for providing data access to user tables.  The SystemDataAccess member is for providing data access to system tables.  This info somes from a response to a question I posted in a sql clr newsgroup at Microsoft.

Wally