The feature is called <a href="https://docs.joinpeertube.org/admin/following-instances#instances-redundancy" target="_blank">"server redundancy"</a> and caches your most popular videos to help serve additional viewers.
Transcoding can also be offloaded to other machines using <a target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/admin/remote-runners">remote runners</a>.