Re: What's the advantage of this pickup arrangement?
These originally came about in the 80's with guys like Vivian Campbell (Dio/Def Leppard).
The guitar in the OP is a Stephen Carpenter signature model. This has been the configuration on these guitars for many years now, per Stephen's request. When Stephen was first starting out, Page Hamilton from Helmet gave jim one of his ESP Horizons which had the humbucker in the bridge and the slant single in the neck. This H/H/Slant SC configuration has been a signature configuration of the Stephen Carpenter model since it was introduced. Shortly after that, he had the middle humbucker added. Stephen has always been a fan of Vivian and the looking his old Kramer's - like the one posted above - and said that he just did it because it looked cool. He also said that he did away with the slant single in the neck because he never used it.
Coming from someone that has the new LTD re-issue Sonic Blue SRC & has done this configuration on a few of the SC-207's (one with passives and the other with actives...), I will say this much about it:
Its definitely a very unique configuration tonally. You get a really unique tone (IMHO) better than a normal B&N position 2 HB middle position in position 2. Its warmer, but it's not muddy like a normal middle position would be typically. And if you experiment with the coil split on both the B & M HB's, you can really get some new diverse tones from that 2nd position.
Position 4 with the middle HB and neck SC is equally unique. If you like darker, warmer and fluid neck positions, then this would be right up your alley! Its hard to describe it... And again, coil splitting the Mid HB will make it a bit cleaner and a bit more Strat-like in this position.