If you are starting out or even seasoned with expressions in Ae, you are probably already familiar with the Expression Controls which can prove useful in production. You may not however be familiar with the Layer Control which can offer specific control over a layer.
Why and how would you ever use such a thing as the Layer Control in Ae?
On that topic, Felt Tips provides a great overview for using the Layer Control in Ae, demonstrating some possible and practical uses. There is also a bit about the special requirements that the Layer Control Expression Controller requires and why that is so.
In all this is a great overview for Layer Control in Ae to get you started, and might have some missed information for users who are already familiar with the Layer Control.