If the plugin does not provide the IPrefetchableSupport interface, the host, depending on its setting, could process it in prefetch mode or not.
In Cubase the user could disable prefetching per plugin if needed…
Hardware based plugins are not processed in prefetch (plugins category is used for specifying hardware based plugins)
In prefetch processing the audio buffers could be larger than in realtime processing and/or could be computed more in advance, this means the time difference between 2 process calls could be faster than realtime (faster than the time corresponding to an audio buffer).
The timing information is then adapted according to how prefetch is working.
This interface allows the plugin to inform the host about it current support of prefetch.