I do not recall any effect in terms of the growth field itself...there was no natural thinning, but then again, my brows were not that thick to begin with. For a while in the 90's, I had the strays waxed about every two months or so, but I do not even remember the last time I did anything other than tweeze the occasional strays (and an annoying grey that shows up every so often). Yes, even lesbians occasionally pay attention to shaping...
Generally, I would expect most people should find the brow to be much like the long-term effect of leg waxing in that growth continues to exist but each successive waxing reduces the rate of regrowth.