Refs

[Gareth Noyce]

References to scalars are no quicker, however arrays and other
data-structures do see a lot of benefit from references. In general I tend
to use references purely for passing closures/tieing events to anonymous
functions and getting around weird TK namespacing issues...

"Advanced Perl" -- chapter one p9-10, discusses reference passing
performance. The last few chapters discuss the internals in more detail...