Wet-on-wet watercolor is when we apply wet paint onto a wet surface. This application method can create seamless gradients and allows for paint to merge into each other without any distinct lines. Wet-on-dry, however, is a more classical way of painting whereby the application of wet paint is usually applied to dry surfaces, resulting in more distinct features in a painting. Wet-on-wet watercolor is good for creating blurred-out backgrounds, gradients, clouds, or anything that has subtle line compositions. Wet-on-dry is good stark features, like trees, animals, and other subject matter that you would like to stand in the foreground.