The idea behind it per the video where they introduced it is that its a means of creators to take ownership of their own content. The idea being that if you follow creator X on youtube you arent actually following creator x you're following them on youtube. If something happens or youtube removes a video for whatever reason of they have to leave the platform then you lose access to their content.

If you're on this app you follow creator x on whatever platform they are on. So in theory it's not just an all in one app but a way to solve the youtube monopoly and make for an easy transition.

In concept I think it sounds really cool, but whether it actually is able to deliver on it's goals remains to be seen.