I don't understand Why there is an overload with IFormatProvider in DateTime.ParseExact ?

If I'm defining exactly how it should be parsed ( spaces , separators etc) , then theres should be no problem :

All these 3 examples show the same result:

example 1 

CultureInfo provider =CultureInfo.CreateSpecificCulture("en-US");
var t=  DateTime.ParseExact("13-2-2013", "d-M-yyyy", provider, DateTimeStyles.None);  
Console.WriteLine (t); //13/02/2013 00:00:00

example 2 

  CultureInfo provider =CultureInfo.CreateSpecificCulture("en-US");
  var t=    DateTime.ParseExact("13/2/2013", "d/M/yyyy", provider, DateTimeStyles.None);  
  Console.WriteLine (t); //13/02/2013 00:00:00

example 3 

 CultureInfo provider =CultureInfo.CreateSpecificCulture("en-US");
var t=  DateTime.ParseExact("13@@@2@@@2013", "d@@@M@@@yyyy", provider, DateTimeStyles.None);  
 Console.WriteLine (t); //13/02/2013 00:00:00

So why do i need to provide provider If I'm explicitly defining the structure ?

c# .net datetime
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