Some games like Megaman 5/6 performed some subtle background effects by performing bank switching on the PPU thanks to the capabilities of the MMC3. That is, the trick is to devote at least two similar 1KB chunks where one contains a subtly changed version of the other. This way, you can simply perform a periodic bank switch and the PPU will render subtly different things every time, without the CPU having to dedicate any resources on changing any values on the data.
A very simple example is provided in blink.s where a character blinks periodically.
