it just creates an array of characters from a supplied string. They just give you the api you have to make a decision where to use it or not. I used it once where i want it to read the string backwards so i made char array using this method and then just looped from last element to first and constructed a new string in reverse order.
public char toCharArray() This function converts the string to a new character array. It returns a newly allocated character array whose length is the length of the string and whose contents are initialized to contain the character sequence represented by this string.