"It's an easy way to obtain high- and low-B+ voltage sources. In fact, there's more than one way to skin a cat... center tapped or non-center tapped transformer using a fullwave doubler. In both cases, the output voltages differ by a factor of 2. The doubler, aside from needing a transformer with only a single secondary winding, has the advantage that the output voltage is 2.828 RMS instead of only 1.414 RMS. So, your secondary can be 177VRMS instead of 354VRMS. Practically speaking, because of resistance losses, the voltage would be somewhat lower under load. And of course, you'd still need whatever VA rating, so the transformer size/weight would be the same.
With either topology, you'll have a significantly lower low-B+, and should you decide to use a regulator, will not have to dissipate as much power in the series resistor."