Is it really important to learn sa re ga ma in singing ? India

Question

I am curious to know if a person has to learn sa re ga ma if he wants to learn singing ?

I heard that Kishor Kumar ji did not learn music or classical. He was a born singer. Is it possible to start singing without knowing the sa re ga ma pa dha ni sa ?

Another example is sunny hindustani who never learner music (as per the Indian Idol) so how come he can sing classical so fluently? This raises my question..