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I had prehaps a bit unjustly tossed the market maker role into that "not real bid/off" bucket. I also agree they do serve to limit the worst case matches. But such a role would simply be unnecessary so I still wonder about the cost in terms of the profits captured by the market makers. Is that a necessary cost in today's world? Not sure.
And I do say that as someone who is fairly active in the markets and have taken advantage of thin markets in the off market hours sessions where speads can widen up a lot.