when does a plugin noConflict get used ?

when does a plugin noConflict get used ?

Have a look at th below function:

  1.  $.fn.carousel.noConflict = function () {
  2.     $.fn.carousel = old
  3.     return this
  4.   }
I read about the jQuer.noConflict() , but i am just curious about how and when would such a function be necessary and how would it be used ?