If I have a feature service with the editing capabilities disabled what can I do with it that I cannot accomplish with a regular Map Service?
I can't think of a purpose for having a Feature Service except for editing. Even if I was building a JS API application and I wanted the geometries I could create Feature Layer object using a MapService URL which would query the service to get the geometries. On top of that with the MapService I have the option of just using a regular dynamic layer in which case I get only the image back.
I also tried using the read-only feature service as input to a geoprocessing tool and that doesn't work either.
The regular Map Service seems to be a lot more flexible than the Feature Service for everything other than editing.