Yeah, it's like assembler (or LISP) macros. It lets you get into the compile phase and do stuff.

I should clarify: You don't have to just store data; you can do anything that Perl lets you do. Create subroutines (or closures). Fire up WWW::Mechanize and load data from a Web server. Build a connection to your database automagically by having a scalar with the connection info in it and an attribute that takes the data, builds the connection, and drops it back into the scalar.