According to the dictionary epilogue means
a speech or piece of text that is added to the end of a play or book, often giving a short statement about what happens to the characters after the play or book finishes.
When I read book sometime I skip epilogue section and finished my reading because it generally have details about what happens to characters and some other details.
But last time when I read 1st To Die by James Patterson, which is a suspense thriller, important details about the suspense were revealed in the Epilogue. The "end" of the book is really good one, and I was originally going to just finish the book and skip the Epilogue, but for some reason I continued with epilogue section. It turns out that there was a twist in the story and that actual suspense was revealed. If I didn't read epilogue, I would've missed actual reason for killing.
Is it common to reveal suspense or other important plot details in Epilogue section? Or is this just a new trend to add a conclusion in that section?
How important Epilogue is relating to the story?
I've read a decent number of suspense-thriller books and this is the only example I've seen so far where there was a conclusion added in Epilogue section.