You don't need two PC's to stream to be a successful streamer, but it does have 2 big advantages:
Tim 'GreyFox' Kazyska is a German Fortnite player who previously played for M10 eSports. He is currently a Twitch Streamer.
For gaming, GreyFox uses a Intel Core i7-7700K CPU with a ZOTAC GeForce GTX 1070 AMP Extreme GPU. He uses a MSI Z270 GAMING M7 motherboard. GreyFox uses CORSAIR Dominator Platinum 16GB memory.
For streaming, GreyFox uses a AMD Ryzen 7 1700 CPU with a ZOTAC GeForce GTX 1070 AMP Extreme GPU. He uses a ASUS Prime X370-Pro motherboard. GreyFox uses CORSAIR Vengeance LPX 16GB memory.