The hydrological processes involve significant complex interactions that simple empirical equations or conceptual models cannot extensively represent. Physical approach models have the capability to simulate these complex hydrological phenomena elaborately and comprehensively, employing parameterization and calibration approaches. Soil and Water Assessment Tool (SWAT), a physically based, spatially semi-distributed and continuous-time step model, is being explored to model these complex environmental phenomena. This chapter aims to review the modelling capacitances of SWAT and the complex situations where the model fails to comply with unless integrated with some desirable modifications. The modifications specific to various complex conditions have been thoroughly reviewed under apposite sections. In this review, it is established that SWAT can potentially simulate varied hydrological regimes with acceptable accuracy. However, it cannot simulate all the pothole parameters in depression-dominated regions and sub-surface complexities of the Karst watersheds. SWAT model simulates the wet periods satisfactorily but performs inadequately in dry seasons, which hamper its utility in watersheds typified principally by low flows. The production and emission of N2O, a critical ozone-depleting gas, are not embodied in the SWAT model, limiting its applicability in providing the comprehensive assessment of agricultural activities on nitrogen cycling. This review will help the researchers to opinionate the suitability of the model to their respective study areas, make suitable alterations befitting the hydrological regimes, and plan the environmental management strategies.