Science disproportionately relies on top researchers to evaluate the work of others, potentially diverting their scarce time from research, mentoring, and other service. We study this trade-off in Italy's national academic qualification system, where evaluators are randomly assigned to committees. Committees with better-published evaluators select candidates with stronger subsequent citation and career outcomes; they also place greater weight on publication impact rather than quantity. These effects partly reflect spillovers within committees: evaluators assigned to serve alongside more accomplished colleagues exert more effort and adjust their criteria. Assignment to a committee, however, reduces evaluators' subsequent publication output and PhD supervision, especially among top researchers. Research losses are especially large in the Social Sciences and Humanities, and among those working in small teams. More productive researchers are also disproportionately less likely to volunteer for service again.