A PhD by prior publication/portfolio allows candidates, who have not followed the traditional academic route towards a PhD, to obtain academic recognition for having undertaken and produced research, and developed their research skills and subject knowledge to doctoral level.
Studying for a doctoral course builds foundations of an academic career as well as enable to develop excellent research skills and become an expert in specific field while pursuing passion.
PhD by publication aimed at academics already in their career, and have not yet completed a PhD. Generally, instead of submitting a thesis written specifically during three/four years study with the university, students are instead required to submit a number of published papers.