DBD backends are the neatest thing since sliced bread. If I want to write a Perl program to use an SQL database, but do not have an RDBMS, there are at least five options I can think of that will use local files as an SQL database. Three of these will give you files you can use elsewhere.
The more tools you learn, the better a job you can do picking the right tool for the job. You might even find yourself using DBD::Excel or DBD::XBase for something that will never interact with the associated applications. Someday I may benchmark all these.
Any others I left out?