Foreword - Afterword

I (almost) only collect Trade paperbacks or Hardcover collections and often there is a foreword and/or afterword by another artist.
I actually never read those as it always seems to be how great someone is, how much they admire him/her, a fan of his work, I feel so honored, blah blah blah.

I was just wondering if anybody actually does read those and what is the value of adding these to a book to you.