Flex ships with number of readymade components. But many times we need components, which can provide custom functionality fulfilling the requirement. This time, we need to create custom components and provide the ability to perform the required task.
Other Benefits of Custom Components:
Custom component also allows you to divide the application into modules. Modules makes the application more manageable, easy to debug and less loading time. You can also collect all your utility Custom components and use it multiple place in the same application and also in multiple applications.