Tutorials/Piston uses

Traps
Disappearing Floor Trap

This trap is created using sticky pistons. Make a tunnel one block wide as long as you want. Under the floor, dig out a 3-block deep pit for each of the trap blocks you want to move. Mine out two blocks horizontally from each space where the trap floor will go and put a sticky piston at the back of each hole. In front of the sticky piston, place the block (make sure that the trap block is the same as the regular floor blocks not being used in the trap so nobody gets suspicious). Carefully place lava at the bottom.


 * This is what it should look like from eye level.

Once done, you can either:

Put a stone (or wooden if you want both mobs and players to die) pressure plate near the trap blocks. Wire it to a not-gate (repeaters are optional so the mob or player will be in the middle of the trap when the floor opens up) and wire the output to the sticky pistons, making them extend. The trap blocks will be pushed forward and will look like part of the floor. Unsuspecting griefers, curious players or mobs will walk onto the pressure plate (if the floor is made of stone, using a stone pressure plate will be camouflaged and players will most likely not see it) and when they do, the floor will open up beneath them, causing certain death to the player from lava damage. The pistons do not have to be reset.

The second option is more efficient but manual. Place a lever somewhere, wire it up to a not-gate and wire it up to the sticky pistons, making them extend. You can place the lever anywhere, even at the other end of the trap so you can watch for incoming mobs or players and flick the lever when they walk on the trap. This requires no repeaters which means that when you activate the lever, the player/mob will fall in instantly.

Farming
Reed Farm



Reeds can be very easily farmed with pistons, in a way that does not require the player to run around smashing each and every reed. Simply align a row of pistons alongside the reeds one block higher than them and run a redstone wire round the back. Connect a button to the wire and you have one click reed harvesting. If you make sure the piston points towards the water the reeds are in and have the water flow towards you, its even less work. And if you are a knowledgeable redstone user, you could make an automatic harvester that feeds into the same water channels as your cactus farms and mob farms. Note that not all the reed items hit the water canal. When the reed is 3 or higher blocks tall, an extra row of pistons may be needed for a more efficiant harvest.

Wheat Farm

When water flows in a straight line path through fully grown wheat, the wheat will harvest itself. Using this property, you can create a spigot by putting a horizontal fully extended sticky piston with a non-gravity affected block on it and by putting a water source above the block. Place a lever that toggles the piston so that when the piston extends, the water source is closed up, but when the piston contracts, the water flows onto the wheat.

Chests
Locked Chests

Create a sticky piston that moves the block above a chest away so that the chest isn't blocked.

Light switches
Pistons can be used to cover and uncover holes with light sources.

Rapid Sand/Gravel Destroyer
Standard Pistons facing towards each other on a blink device can be used to rapidly destroy sand and/or gravel falling into it a an approximate rate of ~8 blocks per second. This design was created by rcmaehl and a schematic of the device along with video are pending upload.