So, the P4-Plugin backup functionality is not configured when Jenkins runs for the first time. This means that the files that change less often are not immediately backed-up once the plugin is configured. I propose adding a "Save All" button. This would allow people to configure the back-up settings at a later date and still have everything they want in SCM.
With that in-mind, it would be really useful to have a set of rules to exclude files. At the moment all builds are backed-up and that creates a lot of unwanted churn on our P4 server.