Randomization ONLY identifies the mean treatment effect. That is, what happened on average. Without further assumptions, it is impossible to identify how many people benefited from treatment and which people benefited the most. If a medical intervention improved the health of people in a village on average, that's great on a surface level. However, with heterogeneity in the treatment response it could be the case that those with the worst health did WORSE from the treatment, and those with the best health did the BEST from the treatment, and their effect offset the losers in magnitude. No policy maker would advocate such an intervention.