Read the <a target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/maintain/configuration#scalability">scalability guide</a> if you plan to have many users or viewers
PeerTube uses ActivityPub because this federation protocol is recommended by the W3C and is also used by other projects like the social network <a target="_blank" rel="noopener noreferrer" href="https://joinmastodon.org/">Mastodon</a>.