The reason one does the full IR is to get the predictability of IFR (airways) flight, namely
- implicit IFR clearance for the whole route (ATC sometimes sound as if they give you a shorter clearance but you can make a fuss if they do that and not get back to you, whereas under VFR you can just pee in the ocean for all the good it might do)
- operating ceiling limited only by aircraft performance (again, ATC sometimes take time to let you climb, but if you say it urgently enough "due weather" they let you go eventually)
- predictable procedures enroute
- ability to land on an IAP if the Wx is not VFR
- ability to depart in sub-VFR conditions from a towered airport
Otherwise, you can just go VFR, and indeed a pilot with balls made of solid brass, a de-iced plane, and willingness to be illegal at times, can go "everywhere" VFR.
But, referring to the topic of this thread, filing IFR OCAS does not give you a single one of these privileges. No enroute clearance, no predictability, nothing.
However, flying under IFR and telling ATC about that does give some privileges e.g. they treat you more seriously and a CAS transit is more likely. But filing an IFR FP does not bring additional advantages because they would not have seen it anyway - unless one is talking about the destination airfield in which case they might like the notice of the IFR arrival.