Applying your styling products (foams & gels) to soaking wet hair is a simple way to maximise the effectiveness of those products and enhance your wave texture.
It's far easier to distribute products throughout your hair when it's wet as the product is applied to each hair strand. Mousses are used to create space between those hair strands, which enhances the wave shape and definition. If you apply product to dry hair, each strand cannot be coated, which limits their effectiveness.
This even distribution helps ensure the product doesn't weigh down specific sections of hair.
Applying products to wet hair also encourages the formation of your waves in their natural pattern. The products then help hold that shape as your hair dries. This results in more defined and consistent texture.