I'll 1) Quickly go over Layer Filters, then 2) Discuss Layer States as in-depth as I can in less than 20 minutes.
Layer States are wonderful and horrible at the same time. To really explain the in's and out's, and all the advantages, pitfalls, and whatever else, I'd probably need to record myself drafting for an hour. I highly recommend asking any questions in the comments below, and even better yet, creating your own file to test these features out for yourself.
