What are good uses for class helpers?

Delphi (and probably a lot of other languages) has class helpers. These provide a way to add extra methods to an existing class. Without making a subclass.

So, what are good uses for class helpers?

I'm using them:

• To insert enumerators into VCL classes that don't implement them.
• To enhance VCL classes.

• To add methods to the TStrings class so I can use the same methods in my derived lists and in TStringList.

  TGpStringListHelper = class helper for TStringList
  public
    function  Last: string;
    function  Contains(const s: string): boolean;
    function  FetchObject(const s: string): TObject;
    procedure Sort;
    procedure Remove(const s: string);
  end; { TGpStringListHelper }
  

• To simplify access to record fields and remove casting.