What is the use of " NumericToNominal" method in machine learning. - machine-learning

Recently i am working on machine learning and build some Models for classification problem with the help of some tutorials. Though i solved my problem successfully but cant get the use and inference of using "NumerictoNominal" method please explain me.
I have tried to learn from the available text but it is very hard core i am seeking for simple explanation.
thanks and regards

I search a lot and finally got a simple example "A set of data is said to be nominal if the values / observations belonging to it can be assigned a code in the form of a number where the numbers are simply labels" for example PIN CODE of a City. Although we use Numeric value to build codes and also u can apply simple Algebra on PIN Codes but it won't make any sense. Also attribute SEX could be male or female it is also a kind of nominal attribute.
thanks

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