It will hinder the gaining of man-boobies.
And prostatitis.
And possibly sebaceous acne.
And edema to your extremities.
Louman is right, it's folks that don't understand how an AI works that causes this huge misconception. People want to be told how much to take of a drug when we all react differently. If you completely crush your E2 (estradiol), yes - it will hinder your gains in a negative fashion. Using it properly (including a blood test to KNOW how much you need) will only give you a better experience, and provide for a better cycle. Estradiol is a carcinogen; while it is necessary for proper function, too much of it is not a good thing by any means.
Of course there are power lifters out there that intentionally allow E2 to raise a bit for that extra water to increase lifts, but that's a different case altogether. For the average Joe, I would strongly suggest keeping that E2 at optimal levels (20-30pg/mL) throughout a cycle.
My .02c