Secondary benefits are byproducts of productive life habits. For example, suppose I start playing some etudes to increase my technical ability, but the whole time I am doing this I am also reading music and thus improving my reading ability on the side. Or if I join the choir for socializing and then also improve my musical ear. I clean my house to feel more at ease here, and the side benefit is ... a clean house. Funny how that works.
A negative activity is less likely to have a positive side effect.