@ebr if the data is stored in a custom location (for example F:\RokuBIFS) , and that location still exists then you would not need to recreate the data if you setup a new server or move media.
Of course if you store the data it in the C:\Users\Username\AppData and your reinstall the OS you would lose the data and have to regenerate it all.
Which is why its a very bad idea to store important information in AppData to begin with.
Chapter images are never stored with the media but has been requested that they be able to for the same reason we store the bif file there - it is basically a visual index of the media itself and it is very expensive to re-generate. Storing it with the media minimizes the situations where they need to be re-generated. If you don't store it with the media and subsequently move your media somewhere else, or just setup a new server accessing it, then these very expensive operations have to run again to create data that already exists.
See above for why it really does make sense. We may end up letting you store these in another location but our default I would suspect would stay as it is for all the reasons I outlined.
If you move to another device, the bif files will have absolutely no impact on the function of that device or app.
Please create a feature request for this and then it will be on the radar. Thanks.