When is it recommended to use data types that pass values by reference?

Reference types in C# are recommended to be used when:

• Objects are large in size, and copying them when passing to methods or assigning would be costly in terms of performance.
• It is necessary for multiple variables to refer to the same object, so that changes through one reference are reflected everywhere.
• It is required to implement complex data structures with mutable state.

For example, classes (reference types) are used to describe entities with identity and state that should be shared across different parts of the program.

Example:

class Person
{
    public string Name { get; set; }
}

Person p1 = new Person { Name = "Ivan" };
Person p2 = p1; // p2 and p1 refer to the same object
p2.Name = "Peter";
Console.WriteLine(p1.Name); // Will output "Peter"

If Person were a struct (value type), then assigning p2 = p1 would create a copy, and changes in p2 would not affect p1.