Hey Guys.
When I got to the end of Block Breaker and ran it on auto-play I noticed that the smoke on each destroyed block would play but the instance would still be in the Hierarchy. Every time a new block was destroyed with smoke particles, the smoke instance would stay in memory. So with a game of 40 blocks that got destroyed 40 instances of the smoke particles would be in memory and in the Hierarchy list doing nothing.
The code below destroys the smoke particle instances after they have finished animating. I have included plenty of comments to hopefully make it easy to understand. The only new bit of code if after the //Destroy The Extinguished Smoke Instance line.
EDIT: The code is for the PuffSmoke method in brick.cs
void PuffSmoke() //Create the smoke
{
//Create a new instance of the smoke in the location of the brick & name it 'smokePuff'.
GameObject smokePuff = Instantiate(smoke, transform.position, transform.rotation) as GameObject;
//Set the colour of the smoke instance called 'smokePuff' to the same as the brick colour.
smokePuff.GetComponent<ParticleSystem>().startColor = gameObject.GetComponent<SpriteRenderer>().color;
//Destroy The Extinguished Smoke Instance
//---------------------------------------
//Create a variable 'smokeLife' to hold the length of time the smoke will be visible.
float smokeLife = smokePuff.GetComponent<ParticleSystem>().duration + smokePuff.GetComponent<ParticleSystem>().startLifetime;
//Destroy the 'smokePuff' instance after it has finished its animation.
Destroy(smokePuff, smokeLife);
} //PuffSmoke() -end`
A big thanks to Baste on the Unity forums who helped me out 
