pyblish starter:
- scene contains data for plugins.
ex a selection group start.model, tells the plugin what to collect for the model instances
see http://pyblish.com/pyblish-starter/

disadvantage: 
- need tools to maintain/create this.
or manually keep selection group up to date.
- requires you to alter scene with metadata

compare with:
data for plugins lives outside maya
- aim is an easier workflow and no changes to original scenes if possible.