I have been working far ahead in my other classes so I finally get some alone time in Zbrush. I'm diving back into sculpting and have been playing around with levels of detail. Zbrush excells at instant subdividing and recalling of subdivision levels.
The easiest way to think of subdiving is to take a square tile. Cut it in half vertically and horizontally and now you have 4 smaller tiles. Keep doing this a couple more times and you'll have a sheet of tiny tiles. Doing this in 3d gives you more detail for an object. The more tiles there are, and the smaller they are, the more refined details can be.
Well Zbrush allows many many levels of subdivions. The image I'm posting below is over 1 million polygons already. What's beautiful is that you can go back down to a real basic level, where say you only have 200 polygons, and bend the overall shape. Then you can go back to the a million polygon model and add small details. What is great is that when you go back and fourth between subdivision levels, you don't lose any detail you added. Say you sculpted a nose beautifully, but found out when you're done with the model that it needs to be an inch higher. All you have to do now in zbrush is go back to the first level and move a couple polygons and violla, the detail nose moves too.