Theoretically, the latency between the streamer and viewers could be zero or near zero.
For playing games online, the minimum possible latency is the speed of light delay. We’re pretty much already at the limit for that one, and we’re even using a lot of pretty clever techniques to mitigate latency such as lag compensation.
Those games are quite well matched with cloud streaming. An example of a game which isn’t suitable for cloud gaming would be competitive FPS games such as rainbow 6 siege, where the additional delay imposed by connection between the player and the game can be quite a significant disadvantage. The only way that this would be low enough to become acceptable would be if you live close enough to the host device that the latency is very low, or or the host device is very close to the game server itself.