It uses WebTorrent for distribution between viewers watching at the same time which can temporarily help with the load on popular videos, but there still needs to be at least one source instance that’s sharing the video “regularly” (for unpopular or old stuff), which ends up having the same bandwidth issues you’d get with any other video platform.
Storage space is one issue. Bandwidth (how many TB/mo goes out the server) is another. And for any “serious” use case transcoding would also be important (so you can keep the other two down for everyone except Apple users who are stubborn to adopt VP9/AV1, and to provide multiple quality options), which unlike the other two requires powerful hardware most instances do not have.