The MakerFarm Prusa i3 and i3v instructions call for the LCD to be mounted to the frame with four M3 screws. If you tighten these screws down, they cause the PCB to flex. If you don't tighten them enough, they rattle and vibrate loose.
These spacers fit between the PCB and the frame, allowing you to tighten the screws as tight as you like without damaging the PC board.
I recommend using nylon locking nuts to prevent the screws from rattling loose over time.
You may also find that the two PC boards can vibrate and buzz against one another. You may wish to solve this by sandwiching foam tape between them and between the front PC board and the frame to reduce vibration further.
I prefer Scotch Extreme Mounting tape for these applications because it conforms well to irregular surfaces and it can usually be peeled off of PCBs and plastics later without making a mess.