Linux is a very important topic for anyone studying forensics. The first, and most obvious, reason is that one might need to examine a Linux machine in the course of a forensic investigation. Linux is quite popular in certain areas of the computing community, particularly in web servers. If you should need to investigate a web breach, there is a reasonable chance that it could include a Linux machine.
Another reason to study Linux is that it is the operating system that Android is based on. The more you understand about Linux itself, the more you will understand Android phones and tablets. Obviously, this single chapter cannot make you an expert in Linux, but it can give you a start.
A third reason to study Linux is due to Kali Linux. Kali Linux is a Linux distribution that is replete with security-related tools. It has gained a great deal of attention due to its hacking/penetration testing tools like Metasploit, and its vulnerability testing tools such as Vega, Sparta, and OWASP Zap. However, for our purposes, the forensics tools in Kali, such as Autopsy, are of more interest.