The ESA SING project evaluates the added value of the Next Generation Gravity Mission (NGGM) and the Mass-change and Geoscience International Constellation (MAGIC) for scientific applications and operational services in hydrology, oceanography, glaciology, climate science, solid Earth science, and geodesy. Using a closed-loop simulation framework that incorporates realistic instrumental, tidal and aliasing errors, synthetic gravity observations were generated to assess the capability of future satellite gravity missions to monitor mass variations in the atmosphere, oceans, hydrosphere, cryosphere, and solid Earth. The enhanced spatial and temporal resolution of NGGM and MAGIC substantially improves the monitoring and prediction of hydrological extremes, including floods and droughts, while estimates of total water storage anomalies, combined with complementary in situ observations and hydrological models, enable improved estimation of key variables of the continental water cycle, including precipitation and total drainable water storage. The improved resolution, accuracy, and temporal coverage of gravity observations are also critical for detecting climate-driven changes in the Atlantic Meridional Overturning Circulation (AMOC). Enhanced monitoring of mass changes in glaciers and ice sheets enable the detection of more rapid melt and accumulation events at finer spatial scales. Improved closure of sea-level and energy budgets is achieved through more accurate observations of mass redistribution at smaller spatial and temporal scales. In solid Earth applications, NGGM and MAGIC increase sensitivity to co-seismic and post-seismic deformation associated with smaller earthquakes while reducing data latency, thereby strengthening geohazard assessment and early warning capabilities. In geodesy, the missions support improved gravity field and geoid modelling, contributing to the realization and temporal evolution of the International Height Reference Frame (IHRF) and to more accurate precise orbit determination. Overall, the ESA SING results provide strong evidence of the scientific and societal benefits of NGGM and MAGIC to prepare the integration of future Earth Observation data into operational services.