The major challenge that a developer confronts when building IoT systems is the management of a plethora of technologies implemented with various constraints, from different manufacturers, that at the end need to cooperate. In this paper we argue that developers can benefit from IoT frameworks by reusing their components so as to build in less time and effort IoT systems that can easily integrate new technologies. In order to explore the reuse opportunities offered by IoT frameworks we have performed a case study and analyzed 503 components reused by 35 IoT projects. We examined (a) the types of functionality that are most facilitated for reuse (b) the reuse strategy that is most adopted (c) thequality of the reused components. The results of the case study suggest that the main functionality reused is the one related to the Device Management layer and that Black-box reuse is the main type. Moreover, the quality of the reused components is improved compared to the rest of the components built from scratch.