Victor Black (and similarly, Joe Jeffrey, who comes from the same school overall) are fans of stuffing proviron into every cycle to, as they put it "alter the androgen to oestrogen ratio".
In short, as mentioned above, the idea is to bind to SHBG, freeing up testosterone to bind to AR, allowing you to have a similar ratio of free androgens to estrogen at a lower total AAS load.
The concept being that if you can achieve a similar Androgen/Estrogen ratio with less total use of Test/DHT-compound, you will have similar anabolic benefit with less downside/toxicity/etc.
This is actually one of the few things I disagree strongly with both of them on, and have actually debated Jeffrey on somewhat extensively.
I'm of the belief that the action of SHBG is still very poorly understood, and that the old school concept of crushing SHBG being inherently good is highly outdated and archaic. I strongly believe that the more we learn about SHBG (much of which we do understand but has been ignored by the BB community for some reason), the more the pendulum will swing towards preserving SHBG to a point. Or at the very least, away from purposefully crushing it.
There's also an underpinning of bitterness and jealousy towards the fact that methods of PED use are evolving rapidly, and towards the people who are pushing that evolution, especially if they're achieving any level of fame or fortune from it.