Cabergoline does almost nothing for progesterone. I think that you and 90% of the public mean/meant to say prolactin. There was a study where it was shown that progesterone was lowered with caber - it was using pregnant women and the lowering effect it had on progesterone was considered non-significant!
and that was by an indirect mechanism where the lowering of prolactin causes a slight lowering of progesterone, though not as great of a effect as lowering estrogen or increasing dht does. Great for controling prolactin though, and recovery after sex. Also B6 does nothing for progesterone, but does for Prolactin.
Now as far as if one NEEDS caber to control a potential raise in prolactin, I wouldn't ever say that it is needed, but might be a good safety procaution or ancillery to boost sexual performance to go with your increased sex drive and aggression. B6 at 200-600mg has been shown to reduce prolactin too, but nowhere close to that of Bromo which is less than that of Caber, but still has an effect.
Of interest is the fact that many quote that B6 causes its lowering through raising dopamine, even though most studies site an indepedant mechanism for it's action and not through raising dopamine. I've been curious as to some sort of synergy of Dbol with Tren or deca as far as the dopamine/progestin thing goes. Dbol and Tren = heaven, so maybe.
And the best thing to control progesteronic sides is to control estrogen.