The performance is no different, and snapshot funcitons may be a little more resource intensive since it writes data to a table instead of a file.
However, there seem to be problems with the some of the snapshot functions in terms of reporting accurate data, or at least in terms of reporting data that is expected. This may be because you cannot reset the monitors like you can with regular snapshots (until the database becomes deactivated).
M. A. Feldman
IBM Certified DBA on DB2 for Linux, UNIX, and Windows
IBM Certified DBA on DB2 for z/OS and OS/390