The needs of the computer user determines if Java must be installed on a PC. If you are a casual Internet user, not having Java installed is unlikely to be an issue.
Custom software made for businesses and educational institutions is often written in Java because of Java's ability to run on any workstation without having to be recompiled for different platforms. Additionally, Java is a popular programming language with independent software developers and is the code base for many free shareware programs available on the Internet. Java is also a popular first language taught to computer science students. If any of these situations apply to you, then Java needs to be installed on your PC.