Step 1: Understand the concept of controlling.
Controlling is one of the fundamental functions of management. It ensures that the organization’s goals are being achieved by monitoring and evaluating performance.
Step 2: Evaluate the options.
- Controlling is not optional; it is an essential and necessary function to ensure goals are met.
- It is also not compulsory in the sense that it is not imposed externally but is an internal, required function for success.
Step 3: Conclude.
Controlling is a necessary managerial function to ensure organizational efficiency.
Final Answer:
\[
\boxed{\text{Necessary}}
\]