Both applications depend on a media library that has to be stored somewhere. If a user is unfamiliar with Linux or just want things work and don’t want to mess around (too much) with OS settings and configurations, using a suitably powerful NAS as a headless server might be a solution too that has the added benefit of also including the needed storage. Having the library on local storage might have some benefits over accessing it remotely (Goodbye NAS, hello USB drive).
PS: I’m using a QNAP NAS as a media server that runs Roon Server and some extensions, Plex Server, Calibre and Calibre-Web.