Unless your Linux machine is an Internet server or gateway machine, there probably will be users on it. Users need to access the system somehow. Either they access the systems across a network using a remote terminal program like telnet, rlogin, or access file systems using NFS. Also, like users typically do on Windows, they might log in directly to the system. With Linux, this (probably) is done from a terminal and the system must be told how to behave with the specific terminal that you are using.
Increasingly people are using graphical user interfaces (GUIs) to do much of their work. With many distributions a lot of the work is still done using the command line, which means they need a terminal, whether or not it is displayed within a graphical window.
In live environments that use Linux (such as where I work), you do not have the access to a graphical interface on all systems (for security reasons, among other things). Therefore, the only way to remotely administer the system is through telnet, which typically requires a terminal window. In cases like this, it is common to move from one operating system type to another (Linux to Sun, or vis-versa). Therefore, knowledge of terminal settings capabilities is often very useful.
When we talk about terminals, we are not just talking about the old fashioned CRT that is hooked up to your computer through a serial port. Instead, we are talking about any command-line (or shell) interface to the system. This includes serial terminals, telnet connections and even the command-line window that you can start from your GUI.