I aways use some amount of AI. I keep it on the low side in the off season and progressively get more aggressive while in prep mode. Yes, you do want estrogen to sensitize the androgen receptor and estrogen is good for adding additional fluid, which allows you to feel more cushion in the joints while lifting heavy, as well as increases strength. At the same time, too much fluid can slow you down, create painful pumps in the low back, or for me in the calves while walking. It can raise your blood pressure. BP control is vital for health in BB. Too many of us have suffered kidney damage from walking around with high BP for too long. Too much estrogen can also create moodiness and make you more likely to store fat. If that isn't bad enough, heres a big selling point. High estrogen can make it difficult to maintain an erection! 

There is a balance to be found with AI use in the off season. An AI will keep test levels higher, as less of your test converts to estrogen. It'll also protect from gyno, for those that are prone. Your dose of gear and type of gear, as well as your sensitivity to estrogen, and your sensitivity to AI's, will determine how much you need. I would start low and see how you respond. For a test only cycle, using 500mg EW, I would start with adex, .5mg 2-3x wk. You can always lower it, if you find you are staying too dry. I have worked with guys that require anywhere from .25mg 2x wk to .5mg EOD to keep estrogen under control. 

Your best bet is to have labs taken to see where you stand. That way, you can pinpoint exactly what you need without guess work