Here is some info I dug up...sorry if it has been coverd before, I just thought it was very interesting:

"However small aromatisation is desirable as estrogen too mediates anabolic activity. It can be responsible for better glucose utilization (repleting lost glycogen stores after exercise) and stimulating increased growth hormone release. But most notably estrogen is responsible for an upgrading of the androgen receptor allowing hormones that act on the androgen receptor to exert a larger anabolic effect. This is why hormones that are strong androgens but also aromatize heavily, like anadrol and testosterone, can put the most mass on your frame."

This was in the description of Equipoise on bb.com