I think it's never really needed in modern OpenACS. My memory isn't reliable, but if I recall correctly back in the Arsdigita days one sometimes had to manually fetch a handle using "ns_db gethandle", which then could be released using " ns_db releasehandle". At some point, OpenACS changed it so that scripts automatically released handles, so the manual practice went out of use.
See here for some old history http://www.eveandersson.com/doc/core-arch-guide/database-access-api
