It would depend mostly on the osmotic pressure.  If the recovery is high and the feed TDS is high, then the required osmotic pressure to make water in the last element will be high. In that case, the feed pressure needed to satisfy the last element will cause the first element to make too much water.  That is when throttling comes into play. Another option would be to have the feed pressure based on the last element of the first stage, and then add a booster pump to provide the additional pressure required for the second stage. A membrane projection would help to guide you for the best option.

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It would depend mostly on the osmotic pressure.  If the recovery is high and the feed TDS is high, then the required osmotic pressure to make water in the last element will be high. In that case, the feed pressure needed to satisfy the last element will cause the first element to make too much water.  That is when throttling comes into play.

Another option would be to have the feed pressure based on the last element of the first stage, and then add a booster pump to provide the additional pressure required for the second stage.

A membrane projection would help to guide you for the best option.