You don't need two PC's to stream to be a successful streamer, but it does have 2 big advantages:
Mark 'letw1k3' Danilov is a professional Fortnite player for Gambit Esports. He can also be found streaming on Twitch.tv regularly.
For gaming, letw1k3 uses a Intel Core i5-8400 CPU with a NVIDIA GeForce GTX 1080 Ti GPU. He uses a ASUS Prime B360-Plus motherboard. letw1k3 uses CORSAIR Vengeance LPX 16GB memory and a Samsung 970 Evo 250GB SSD for storage.