The main advantage of a client-server architecture over the file-database architecture is that it is possible for multiple users to share the same database at the same time. It is also possible to connect to your database via a network, without the need to create a file share.
There is a performance hit as can be seen in this comparison table: http://h2database.com/html/performance.html
More information about client-server architecture can be found here: http://en.wikipedia.org/wiki/Client-Server