It looks like he's trying to get the pump at max flow, while restricting output of A. The remaining flow goes through B.
I would think you could probably get away with just the valve on B, since that's the easiest path for the water (pipe size being equal). Personally, I would build it with both just in case. For the extrat $5, it saves you the possibility of having to rework it later, possibly wasting other fittings in the process. You can use the valve on A to stop back-siphoning during planned pump stoppages, if nothing else.