Where Should We Not Use WorkManager?

WorkManager is designed for discrete, “transactional” tasks, not ongoing work. So, for example, WorkManager is not designed to play music continuously in the background. A foreground service is the solution to use for that, with background threads as needed (e.g., for disk I/O to read in the playlist details).

WorkManager is designed for work that will happen sometime, but not at some specific time. If you need to get control at a specific time — such as to alert the user about an upcoming calendar event — use setExactAndAllowWhileIdle() on AlarmManager.

WorkManager is designed for work that will happen eventually, but perhaps not immediately. If you have background work that has to be done in real time in response to user input (e.g., download the video that they just purchased), use a foreground service.

WorkManager is designed for work that might happen completely asynchronously with respect to your current process. Hence, it is not useful for cases where the work that you are doing only affects the current process, particularly its UI. So, for example, downloading avatar icons to display in your app may not make sense once the UI is gone, as you may never need those icons. For that, use a thread pool, reactive solutions (e.g., RxJava), or libraries that in turn use those sorts of things.