MiniSearch addresses use cases where full-text search features are needed (e.g. prefix search, fuzzy search, boosting of fields), but the data to be indexed can fit locally in the process memory. While you may not index the whole Wikipedia with it, there are surprisingly many use cases that are served well by MiniSearch. By storing the index in local memory, MiniSearch can work offline, and can process queries quickly, without network latency.
A prominent use-case is search-as-you-type features in web and mobile applications, where keeping the index on the client-side enables fast and reactive UI, removing the need to make requests to a search server.