Defects can significantly modify the electrical and optical properties of quantum well (QW) structures based on InGaN. We present an overview of our recent results on the properties of point and extended defects in InGaN/GaN QW devices. By analyzing single-quantum well (SQW) devices, we show that: defect density is higher in indium-containing layers; also, the use of an indium-containing underlayer can significantly reduce the density of traps in the active region of the devices, resulting in a better device efficiency. The properties of defects can be effectively extracted by deep-level optical spectroscopy. Furthermore, by studying multiple QW samples with a high number of periods, we demonstrate that: a) extended defects, and related V-pits, may locally modify the current distribution across device area. A TCAD model has been defined for numerical simulation of conduction near V-pits. b) the presence of agglomerates of V-pits may result in a locally increased photogenerated current density; also, we identified a significant redshift in emission wavelength in proximity of agglomerates of V-pits, surrounded by trench-like defects. This article provides a wide range of results for a better understanding of the properties of defects in InGaN/GaN devices.