When to use Builder Design Pattern?

The Builder design pattern is used when you need to create complex objects with a large number of optional components or configuration parameters. This pattern is particularly useful when an object needs to be constructed step by step, some of the scenarios where the Builder design pattern is beneficial are:

• Complex Object Construction: When you have an object with many optional components or configurations and you want to provide a clear separation between the construction process and the actual representation of the object. 
• Step-by-Step Construction: When the construction of an object involves a step-by-step process where different configurations or options need to be set at different stages.
• Avoiding constructors with multiple parameters: When the number of parameters in a constructor becomes too large, and using telescoping constructors (constructors with multiple parameters) becomes unwieldy and error-prone.
• Immutable Objects: When you want to create immutable objects, and the Builder pattern allows you to construct the object gradually before making it immutable.
• Configurable Object Creation: When you need to create objects with different configurations or variations, and you want a more flexible and readable way to specify these configurations.
• Common Interface for Multiple Representations: When you want to provide a common interface for constructing different representations of an object.

The Builder Design Pattern is a creational pattern used in software design to construct a complex object step by step. It allows the construction of a product in a step-by-step fashion, where the construction process can vary based on the type of product being built. The pattern separates the construction of a complex object from its representation, allowing the same construction process to create different representations.