The impact of fractal�percolation system, built into quantum-dimensional light-emitting InGaN/GaN and AlGaN/GaN heterostructures, on the carrier transport, non-radiative and radiative recombination, current crowding effect, and peculiarities of degradation process is shown. The system forms in the extended defects and 3D fluctuation in alloy composition. The properties of the system depend significantly on the degree of the nanomaterial disorder and the injection current value. The quantitative determination of the degree of disorder in InGaN/GaN and AlGaN/GaN light-emitting heterostructures by the use of multifractal analysis allows us to investigate the correlation between electrical and optical properties of light-emitting heterostructures and the degree of the nanomaterial disorder. As a result, an increase in lateral and vertical carrier transport and crowding effect with increasing degree of disorder was clarified. The threshold-type dependences of the external quantum efficiency in light-emitting diodes on the degree of disorder and threshold-type dependences of the spectral low frequency noise density on the injection current were also investigated. The existence of fractal�percolation system with nonlinear properties limits the use of the ABC model in the analysis and simulation of thermal processes, calculation of the emitted power loss with increasing current density, and interpretation of external quantum efficiency degradation mechanisms in LEDs. This phenomenon causes contradictory experimental data and conclusions in scientific publications concerned with these materials. It is also responsible for various unsuccessful efforts to apply the commonly accepted models to describe the external quantum efficiency droop and for the unpredictable failure in InGaN/GaN and AlGaN/GaN LEDs