There is not really a technical advantage at all, it ultimately is just cheaper (cost/ real-estate) because your not using two transformers/ dual taps etc. I agree with Glenn on this one, series heaters although used in earlier designs is NOT the best way to run heaters.
Cheaper (cost/real estate) is not good. Especially when an amp starts to blow out expensive rectifiers because of that. Glenn is good at spotting ways to improve amp schematics. When I sent him one of my commercial amps in for mods (not a Woo) he discovered several errors in the wiring and fixed it. I really trust Glenn's expertise in understanding amp designs be it his or others. The proof has always been in the pudding; his amps sound great.
Edited by Clayton SF - 10/27/13 at 12:40pm