.30 Browning 1917 vs .30 Browning 1919 Machinegun

I've often wondered once the 1919 came into being, why the water cooled 1917 remained in production. I would think the portability factor alone would have been a tremendous plus. I can only assume that the 1917 could probably with its water cooled system allow for more sustained fire. But it's a complete assumption on my part.

Could anyone shed some light on the differences between the two. What makes one better than the other and why would a unit choose to deploy one over the other?

Thanks

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