To allow your mobile device to be used as a wireless remote camera.
To pull in other people's video and audio for podcasting/broadcast (guest appearances)
For sharing high-quality and low-latency audio and video across the Internet and within LANs.
Bring a friend's remote game stream into your OBS and do side-by-side gaming together.
For VR chat applications
For high-quality audio streaming, including remote DJing
Wirelessly stream video from any pro camera using just a $10 Raspberry Pi and HDMI adapter.
For sending any streaming-data peer-to-peer over the Internet in a few lines of code, including JSON.
To allow you to publish to YouTube with your smartphone even though you don't yet have enough followers to broadcast to Youtube with the YT mobile yet.
To watch movies with friends, via screen sharing, privately, and with low-enough latency to talk on the phone together while watching it.
Use as a remote low-latency teleprompter feed.
Recording remote or local video at high quality without needing any downloads.
Remotely streaming MIDI device output, such as MIDI keyboards or production control boards.
Controlling OBS remotely from any computer on the Internet using VDO.Ninja as a p2p bridge.
Recording remote participates during interviews directly to their own computer; perfect recordings.
Applying green screens, digital face effects, and other advanced video filters to video streams.
Real-time closed-captions and transcriptions.
For whatever other reason you might come up with.