Hardening Linux: Service Shutdown!

I am developing a security guide to provide recommendation to harden a Linux box after a base installation. One of the basic steps to harden a Linux box is to evaluate all Services and shutdown anything that is not necessary for the operation of the operating system and services it offers to its clients. Shutting down Services provides the following benefits:

• Decreases boot up process resulting in higher uptime
• Less system resources are consumed which increase the overall performance of server
• Removes / reduces the risk of any Service vulnerability or abuse

To accomplish this you should know about the functions of each and every Service. There are different documents available to explain this. Here I have found something that helped me a lot because my document is based on Redhat I have found this matching my requirements the best:
Understanding Your Redhat Enterprise Linux Daemons