Light Userdata Question (Lua5)

["Michael T. Richter" <mtr1966@...>]

I'm a little confused by light userdatas.  When, exactly, would I use these
given that I'll never know when they're collected?  I was thinking they're
for things like file handles, etc. -- but all of these involve resources
you're going to want to reclaim once they're no longer used.  Yet light
userdatas are the userdata type that can't be reclaimed....

When would I want to use light userdatas instead of full-fledged ones?