Photocatalysis, by harnessing solar light to drive essential chemical transformations, is recognized for its transformative potential in sustainable energy production and environmental remediation, addressing critical global challenges such as CO2 reduction, water splitting, ammonia synthesis, etc. The development of novel photocatalytic composite materials is crucial, not only enhancing reaction efficiencies but also enabling more effective utilization of solar energy, thus propelling the field towards practical and scalable solutions. Among these materials, composites such as boron (B)-doped titanium dioxide, B-doped graphene, and B-doped carbon nitride are distinguished by their exceptional performance in various photocatalytic reactions. These enhancements are primarily attributed to the unique electronic structure of B, its small size and electron deficiency facilitate improved carrier detached and diminished regrouping rates, thereby expanding the spectrum of light absorption. Despite considerable advancements, the specific role of B within photocatalytic systems remains ambiguously defined, with ongoing research yet to conclusively determine whether B functions primarily as a catalyst (a key) or merely as a supportive enhancer (an auxiliary). Addressing this gap, this review adopts a novel analytical perspective, investigating the electron-deficient nature of B to elucidate it's in photocatalysis distinct advantages, potential regimes, and practical applications. The review further delineates the current dilemmas and articulates future directions within the photocatalysis. By aiming to systematically characterize B's role in photocatalytic processes, this comprehensive review offers essential scientific and practical insights, pivotal for the development of more efficacious, innovative photocatalysts. Enhancing our understanding of the underlying mechanisms in photocatalytic reactions, this work substantially contributes to the achievement of sustainable development goals and establishes a foundation in this critical area for future.