Using a key/value pair allows you to create key-value lists (maps) and retrieve values from them by using a string inside the operator (instead of a number).
Example 1 - Adding values by key
string [] fruitColor; fruitColor["Apple"] = "Red"; fruitColor["Banana"] = "Yellow"; fruitColor["Orange"] = "Orange";
Example 2 - Retrieving values by key
return fruitColor["Banana"];