These bars are more concentrated than traditional shampoos and conditioners, so you can use less per application and they will last longer. This is especially true with proper care (don’t be letting your bars soak in water, and don’t store them in travel tins for any length of time)!
Shampoo bars are great to travel with, as you don't have to worry about any potential for spillage or liquid restrictions. The bars are perfect for carry on as they are small and lightweight.
Shampoo bars can also be used for other purposes like washing your body or your pets