Fast control afforded by power electronics in highvoltage direct current (HVde) systems, especially voltage-source converter (VSC) based HVde systems, needs to be carefully assessed to identify stability boundaries. While there are several averaged models of VSC-HVdc systems that have been studied with low bandwidth alternating current (ac) system models, there have been limited studies to show the need for high-fidelity models to understand the control interactions between different VSC-HVdc systems as well as with other grid components. In this paper, the fidelity of power electronics and connected grid components like transmission lines are identified based on defined use-cases to understand the stability and impact of the fast control afforded by VSC-HVdc systems. These results will be useful to understand the methods required to study control in VSC-HVdc systems.