I'm also curious about Developer Mode, what advantages does it offer the developer? I did find an older post that gave a url to execute to turn it on, and I also saw options for it in the Info.plist file, but there really wasn't anything explaining what it does for the developer? :P
Url: (I'm assuming this enables dev mode for the server)
There’s really not much benefit to either. On the server, it will allow downloading beta builds of the plugin Framework. Generally, it’s recommended that you develop against the release framework since that’s what your users will be using.
For the channel, setting the devmode flag in the plist is supposed to prevent PMS from auto-replacing the bundle with the “official” version. This is only beneficial when you’re working on a plugin which is already available in the Channel Directory. It has the same desired effect as the more common practice of sym-linking the plugin bundle.