One advantage of two drives is you can make a BACKUP IMAGE of the SSD (i.e. Acronis True Image) in case of failure or data corruption.
A 256GB SSD is good enough for Windows and apps (should come to under 100GB) with at least 100GB left for some games.
Not all games really need an SSD. It helps with load times, so aside from a few seconds on the initial load for most games, it's biggest help is a game like SKYRIM which has lots of loads (jump around map, enter building or dungeon).