It all depends how your body adjusts to each time you cycle. AND the duration of time BETWEEN cycles. If you give plenty of time off to refresh your receptors, you may be able to stay at the same dosage every time. But what happens most often is that people will find that they need to bump up the dosage a little more than the last time if they are looking to add a lot more muscle, specially for a bulker. Also, they wait the bare minimum between cycles too. But if you're cutting for instance, then the same dose should be fine for preserving lean muscle.
Personally, I always stayed at 500-600/wk because any more than that and I would get very bloated. But this time around I'm sticking to arimidex EVERY day at .5mg throughout my cycle and I was able to bump up to 750mg/week (for a cutter!) and it's working awesome! Better than I imagined. No bloat, shredded like never before. Actually, I am looking my best right now and couldn't be more satisfied. Oh, and 600 mg of deca too. I've been getting bigger and bigger and believe it or not, I actually have been gaining very little weight. (That was the goal.) I went (so far) from a size 33 waist to a size 31 waist in eight weeks and I can count all 8 of my ab muscles! Veins like a road map! Love it!