I would like a plug-in that deletes the source file from your calibre library after a conversion. I only use one format and have no need for the other formats to remain included in my Calibre library.
I have asked for this to be added to the program with many negative responses, "people will flame spray the developers if they lose their originals" so if it can be added as a plug-in then people would have to go out of their way to add this option and if they lose originals this way it's their fault.
One person even suggested that I write the plug-in on my own but unfortunately I am clueless when it comes to that, but I did make this nice picture of how I would like to see the option added.
If someone could write this plug-in I would gladly contribute to their paypal account.