Seaweed offers a wide range of interesting bioactives. With over 10,000 species globally, it is of great interest to be able to extract these compounds. Hence, seaweed fractionation into a wide spectrum of valuable products using multistage cascade processes offers a sustainable approach of exploitation of this resource to produce bioactive ingredients, chemicals and biofuels. This biorefinery processing approach should be adapted to local conditions to maximize the biomass utilization and to lower the waste fractions or preventing any waste materials re-enforcing the circular economy. This review presents an overview of the potential uses of waste generated after seaweed processing for food and other uses, as well as the utilization of invasive species biomass and other invasive species.