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Estradiol (Estrogen) is a hugely important hormone which is found more abundantly in women.  It is important to note that this hormone is also found in men, just in far less quantity; which is a similar concept regarding testosterone in women.

Estradiol is important in a variety of functions throughout the human body, not only regarding the reproductive system, for which it's much more widely known for. 

Regarding exercise and estradiol, it's not nearly as important or effective in promoting performance and body composition (positive changes).  Some definite positive things that estradiol promotes is a healthier cardiovascular and nervous system.  The hormone has protective effects which would be why cardiovascular disease (and neurological diseases) are less evident in younger women rather than older women, when estradiol levels fall. 

Body compositionally, estradiol does not have many of the same positive effects that testosterone has.  While testosterone promotes an increase in action potentials (nervous impulses), estradiol doesn't have that same effect.  Testosterone can promote a larger muscle structure, which is why men are typically larger than women.  Estradiol can promote an increase in body fat, which is why women typically have greater amounts of body fat than men.  This increase isn't necessarily a bad thing, however, it does have an important factors when it comes to children, which men cannot support via biology. 

Performance-wise, estradiol doesn't have a significant impact.  Body composition-wise, it can.  If you regularly assess your body composition, you may find that there are fluctuations each month (I wonder why?).  In any case, estradiol is necessary for good health, for both men and women.