If you are going to use objects to access a database, then Class::DBI will typically make that easier and save you code. Before I started using it, I would write my own data access objects from scratch. Class::DBI has made that unnecessary, or at least removed the boring parts of it.

I don't think that the usefulness of Class::DBI for a particular application has much to do with the size or complexity of your database. I do think it has a lot to do with your approach to coding and whether or not you like accessing your data as objects.

When I've used Class::DBI with HTML::Template, I found it pretty easy to copy data from a list of objects into a hash structure that H::T could handle. I definitely was writing code to handle that translation, but that's the price you pay for the strong abstraction layer that H::T provides you. If you want a templating system that doesn't require you to arrange your data like this, Template Toolkit is happy to work on Class::DBI objects directly.