Well my 600 does not have it in and the oil flows and returns fine. the return is just a dump back into the crankcase.
I think oil cooler lines getting blocked are akin to having ones arm broken by a Swan.
Very few people know of it ever happening.
Just been having a constitutional rethink on this, it can only be a partial restrictor to maximise flow out of the cooler port, as without it both the filter port and the cooler outlet maybe of similar size. I'll look at installing one now. Perhaps. :-)