When to consider a dedicated streaming PC is the longer-term equipment-upgrade decision that most streamers reach in year 2 or beyond. The dedicated streaming PC handles the encoding work on a separate machine from the gaming or content-production work, which removes the resource competition that single-PC streamers fight.

The signal that a dedicated streaming PC is justified: the streamer is running CPU-intensive games or production software that competes with OBS for resources, frame drops happen during high-CPU stream moments despite hardware encoding, or the streamer is producing high-bitrate output that exceeds what a single-PC setup can sustain cleanly.

The architecture: the gaming or content PC outputs to a capture card on the streaming PC, the streaming PC runs OBS and handles encoding, the audio is routed via cable or virtual audio devices between the two PCs.

The cost is meaningful (a second PC plus capture card), and the complexity adds an entire failure mode to the operation. Justify it with metrics, not with prestige. Most streamers do not need it.