If You Don't Document It, It Never Happened

"The Department of Labor does not like people being fired without a company following its own termination policies and creating a paper trail along the way....

The easiest way to document poor performance is through regular performance reviews....

Yes, writing expectations takes work.
Yes, it takes away from production time.
Yes, it is not urgent.
Yes, it is very important.

As a side benefit, creating written expectations and job descriptions goes beyond protecting oneself from lawsuits.

The process of thinking through what is expected of the various positions in your operation creates a clear picture in your mind of the ideal workplace. And the clearer you can see it in your mind, the easier it is to create in reality..."

Read more in this post from Management-Issues.