Attached Link: http://superuser.com/questions/150012/what-is-the-difference-between-local-and-roaming-folders

Windows has a local and a roaming folder in AppData. Those have different purposes that become significant when in a networked situation with roaming user profiles.

Assuming you have a roaming user profile and several machines on which you can log in with that account and use Poser. There are certain files that you'll want to have in the roaming profile: the preferred scene, preferences, UI layout, recent renders. Other files you want to keep local and not roaming: the render texture cache, temp files for undo, shadow maps or temp files for dynamics calculations.

 That is why FireFly writes the result of a render to the roaming folder: it is not disposable temporary data, it is valuable user generated data that you would not want to have thrown away by a disk cleanup tool.

 In either case, the overhead from writing that file is negligable compared to what else is going on during a render and very unlikely to be a limiting factor for your render speed.