newbie conceptual question

Greetings, I have been programming with imperative languages for 15 years. Now I started learning Haskell, and functional programming (and I am very determined to learn it well). It seems to me that I can still use functional programming paradigm with an imperative language. How can I benefit more from a functional programming language (i.e.Haskell)? In other words, is having built-in language constructs for functional programming the only reason for using a functional programming language(I can use polymorpim, and generic programming in imperative languages, as well). Thanks