The present paper reviews the concept of wire arc additive manufacturing (WAAM), its associated defects, and the existing post-processing methods for product quality enhancement. The application of friction stir processing (a surface modification technique) for enhancing the microstructure and mechanical properties of wire arc additively manufactured parts was considered as a new horizon in this field of research. Finally, the article concludes that the widespread usage of WAAM is still challenged by some obstacles, which may need to be targeted and addressed in unique ways for different materials in order to generate functional systems in a reasonable amount of time. Unifying materials and manufacturing techniques to produce defect-free and structurally robust deposited parts will become increasingly important in the future.