The HADES spectrometer installed at GSI Darmstadt was designed to measure \(\mathrm{e}^+ \mathrm{e}^-\) pairs (dielectrons) in the SIS/BEVALAC energy regime. Thank to excellent particle identification capabilities of the detector investigations have also been extended to strangeness production providing an unique opportunity for a new insight into properties of nuclear matter at large baryon densities and moderate temperatures. A dedicated programme focusing on systematic investigation of dielectron production in nucleon-nucleon, proton-nucleus and heavy ion reactions brings many important and surprising results. The studies performed with elementary reactions demonstrate sensitivity of the \(\mathrm{e}^+ \mathrm{e}^-\) probe to the extended structure of baryonic resonances and calls for more theoretical studies. On the other hand, a direct comparison of the nucleon-nucleon data to the one obtained in more complex systems allows for isolation of true in-medium effects which is related to baryonic sources with resonances playing again a key role. In the strange sector intriguing new results on \(\phi\) and \(\Xi(1321)\) production were obtained. Futhermore, precise data on transverse momentum distributions of neutral kaon indicate sensitivity to in-medium kaon potential. In the talk overview of the results and perspectives for future investigations will be presented.