A function is a group of statements that exist within a program for the purpose of performing a specific task. A program benefits in the following ways when it is modularized:

Simpler Code - A program's code tends to be simpler and easier to understand when it is modularized. Several small Functions are much easier to read than one long sequence of statements

Code Reuse - Functions also reduce the duplication of code within a program. If a specific operation is performed in several places in a program, a Function can be written once to perform that operation, and then be executed any time it is needed. This benefit of using Functions is known as code reuse because you are writing the code to perform a task once and then reusing it each time you need to preform the task.

Better Testing - When each task within a program is contained in its own Function, testing and debugging become simpler. Programmers can test each Function in a program individually, to determine whether it correctly performs its operation. This makes it easier to isolate and fix errors.

Faster Development - Suppose a programmer or a team of programmers is developing multiple programs. They discover that each of the programs. The discover that each of the programs performs several common tasks, such as asking for a username and password, displaying the current time, and so on. It doesn't make sense to write the code for these tasks multiple times. Instead, Functions can be written for the commonly needed tasks, and those Functions can be incorporated into each program that needs them.

Easier Facilitation of Teamwork - Functions also make it easier for programmers to work in teams. When a program is developed as a set of Functions that each performs an individual task, then different programmers can be assigned the job of writing different Functions.