What is an easy way to understand the reasons why functions use up CPU time and incur expenses?

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Functions use up CPU time and incur expenses for a variety of reasons, such as:

1. Computation: When a function performs calculations, it requires CPU time to execute those calculations.

2. Memory allocation: When a function needs to allocate memory for variables, data structures, or other objects, it incurs expenses.

3. Input/output: When a function reads input from a file or user and outputs data to a file or screen, it takes up CPU time and incurs expenses.

4. Control flow: When a function executes conditional statements, loops, or other control structures, it requires CPU time to evaluate those conditions and perform the appropriate actions.

5. Call stack: When a function is called within another function, it adds to the call stack, which requires additional CPU time and memory allocation.

Understanding these reasons can help developers optimize their functions for better performance and reduce expenses.