Perceived Value
Hardcovers (Case Bound) immediately command a higher price point. They feel substantial and collectible. If you are doing a Kickstarter special edition, Hardcover is the way to go.
Cost Efficiency
Softcovers (Perfect Bound) are significantly cheaper to produce and lighter to ship. For your standard trade paperback or manga volume, this is the industry standard.
Durability
Hardcovers last longer, but modern softcover laminations (like soft-touch matte) are very resistant to wear and tear.