There's limited benefit to putting games on an SSD. You will get faster load times. In lots of games, particularly multiplayer games where you have to wait for everyone to load in before starting, that's entirely irrelevant. For some games it is nice. Witcher 3 for example, can take a long time to load a save on death, or fast travel to a new location. I would have loved to have Witcher 3 on an SSD. But in the end of the day, it's definitely not essential and should only be considered if you have a healthy budget and an otherwise high end system with no obvious upgrades required.
If you've decided you do want your games on an SSD, then you're almost certainly better off with a single large SSD over two smaller ones. Larger SSDs are...