Data sharing has become a default requirement made by an increasing number of research funding and research performing organizations. Data should be findable, accessible, interoperable and reusable, in an as open as possible way, is the adagio of today. The idea is that the research system will be more efficient if data sharing will be part of the dominant research culture. This should lead both to a greater transparency of research, because FAIR data can be checked and will contribute to replicability of research. And for researchers it will make it possible to stand on the shoulders of predecessors, opening possibilities for comparative research or answering new questions on the basis of existing data. This is the theory. But in how far does the above serve the needs of the users? In how far is data that is offered for sharing actually being reused? And in how far do “old” data contribute to new knowledge creation? Actually, not very much is known about the reuse of data, and even less about how this reuse leads to new scientific insights. Although recommendations for citing data abound, it even appears to be very hard to trace back reused data in the literature. The core of this paper is on the use of a national data service, taking the EASY repository of Data Archiving and Networked Services (DANS) in the Netherlands as a case study, and presenting a quantitative overview for the period 2007-2019.