Hi @ele, lovely to read you here too!
Disclaimer: the information I am about to give is not 100% sure, I am definitely not an expert.
One of the most awesome features of PeerTube, from which it also gets the name, is that if multiple people watch the same video, those viewers also upload to others the bits of video they have already downloaded. Therefore, if many people are streaming the video at the same time, it becomes a bit like bitTorrent: many peers downloading the video from multiple sources and uploading it to others, too. You can notice this is happening because when you watch any video on PeerTube you can see in the bottom-right corner the download and upload speed metrics and the number of peers:
In this way, the load on the server is automatically reduced because the video is not streamed from one source only, and you don’t have to worry about server load 
(in this particular case only, in general we definitely should worry about server load and this is something I am trying to understand myself 
)
I hope it makes sense, I am still waking up 