You don't need two PC's to stream to be a successful streamer, but it does have 2 big advantages:
'Tinny' is a full-time Twitch streamer and content creator. He is currently focusing on Fortnite.
For gaming, Tinny uses a Intel Core i7-8700K CPU with a ASUS ROG Strix GeForce GTX 1080 Ti GPU. He uses a ASUS ROG Maximus X Hero motherboard. Tinny uses G.SKILL Trident Z RGB 16GB memory and a Samsung 850 EVO 250GB SSD for storage.