Why do we need multitasking functionality in an operating system?

Multitasking is a process in which we do multiple task at a time.    

In computing system, multitasking is the concept of performing different types of multiple task and process over a certain period of time by executing simultaneously.

Operating system basically allow various task to run simultaneously by the user. In an operating system, each task consume storage system and all the other resources.

Multitasking function facilitate memory isolation in the processor and also supported different levels of security system in the operating system. For example, "a programmer working on any program in a system and as well as listening the music then, it perform multiple task at the same time".