They are not useless, but they need an address and data bus and some additional control signals and your arduino has none of that.
Now, you could add that using latches, bus transceivers or other logic, but it might get tricky to get the clocking and timing right.
If you don't continually refresh it fast enough, any data you store will slowly disappear. You also need to convert all signals to 3.3V or run the arduino on 3.3V.
Even if you get it up and running, you can't use it for code, since the AVR only supports executing code from its built in flash. Using it for other data is fine of course.
If you abandon AVR and move up to ARM, there are many more microcontrollers available with built-in memory controllers that have SDRAM support. Still, low end parts in packages with few pins are unlikely to support external memory of that type.