Any ideas about how important offensive flow actually is?
That's not really the best way of looking at it. Offensive flow itself is a reflection of the passing/handling skills, weighted based on which position the player is in. But if you have, say, two guards out there with very high passing/handling skills, you'll have great offensive flow, but if you dump it in to a 3C team and all three bigs have atrocious handling and passing, they'll still turn it over a lot. Likewise, if you have good passing and handling throughout the roster without having exceptional values on the guards, the OF will be lower but you'll likely be more effective than the rating might otherwise indicate.
The long and short of it is that OF is a measurement of the skills used, not something that the engine itself would look at to calculate play results. The better way of looking at it is "how important is passing and handling, for each position?"