What is the purpose and role of side effects in programming?

Side effects in programming are changes in the program's state or interactions with the external world that occur during the execution of a function or operation, beyond returning a value. They are important because they allow the program to interact with the environment: modifying data, working with files, networks, databases, displaying information on the screen, etc.

For example, a function that writes data to a database has a side effect — changing the state of the database. In functional programming, efforts are made to minimize side effects to improve code predictability and testability, but in real applications, they are necessary for performing useful actions.