whats the diffrence, can they be used together or just separately ?
The VFS layer is what is used to turn the internal objects in rclone into something which looks like a file system - hence VFS - Virtual File System.
rclone mount always uses the VFS regardless of the backend.
I guess you are asking which features of the VFS you can turn on. The answer is that they shoud all be compatible with the cache backend. Some features you shouldn’t turn on with the cache backend - eg
--vfs-cache-mode full as then you are caching everything twice, but you can if you want to.
As I have been using unionfs rclone mount with a local upload folder, was wondering if the cache could handle the same way and but then was playing with it was trying to figure out a way for file changes to be detected right away. Rather than waiting so that say Plex autodetection would work. As using other scrips to detect changes is over complicating things.
Edit so I think I found the options I wanted but leads me to think what happens when say a server is reset and or power fails also does it meaning how much less reliable is it than using the rclone copy/move commands.