Functional programming matters

During the reading of Scala in action, I found the reference link quoted by the author(Nilanjan Raychaudhuri), which is an introductionary article about functional programming. I’ve learned that functional programming is minority compared to object oriented programming, which means it is not popular, but being a curious programmer, I am eager to know for a long time why it has its attractiveness, where it is being used and how it can be used to solve real world problems.