When writing JavaScript, you often need to perform the same action in multiple places. Without functions, this means copying and pasting the same code again and again. This repetition not only makes your code longer and harder to read, but it also increases the chance of mistakes. If you need to change how something works, you have to find and update every copy, which is time-consuming and error-prone. Functions solve these problems by letting you group code into reusable blocks. You can call a function whenever you need it, so your code stays organized, easier to read, and much simpler to maintain.

In real-world projects, functions are essential for keeping code manageable as your application grows. Imagine building a website where you need to validate user input, calculate totals, or display custom messages in several places. By putting these routines into functions, you only have to write the logic once. If you ever need to fix a bug or add a new feature, you can update the function and instantly improve every part of your program that uses it.