Post- or pre-processing of assets is very useful if you have custom-made or complex assets that need additional work once they are imported in Unity. In most cases, this is not needed as Unity does a lot of work for you by processing assets already.

We won't go into too much detail here as it is a very large area; this section is mainly to highlight its existence for those who were not aware. It is well-worth reading and checking up on.

A more interesting area for study, especially if you are working with many platforms and find yourself doing repetitive tasks on each platform (or when you create your Unity assets and need to copy files to a platform to work), is the ability to extend Unity3D's own project build process.

Simply create a normal class script in AssetEditor, and then create your build action function with the [PostProcessBuild] attribute and the build function signature, as follows:

using UnityEngine;
using UnityEditor;
using UnityEditor.Callbacks;

public class MyBuildPostprocessor
{
  [PostProcessBuild]
  public static void OnPostprocessBuild(BuildTarget target, string pathToBuiltProject) 
  { }
}

The attributes from the build processing give you the following information:

You can also control the order in which this function is processed by adding parameters to the [PostProcessBuild] attribute as follows:

[PostProcessBuild(10)]
public static void OnPostprocessBuild(BuildTarget target,
 string pathToBuiltProject) 
{ }

The order number is a definition of priority: the higher the number, the lower the priority. By default, all scripts have a priority of 1. Scripts with lower numbers are executed first (even negative numbers such as -10 are allowed for ultimate priority), whereas scripts with higher numbers are executed last.

This is especially useful if you want to have several actions execute on a successful build and want to control the order in which they are executed.

MyPlatformClassFile.cs.ignore

For more information about build processing, see the Unity scripting reference guide at http://docs.unity3d.com/412/Documentation/ScriptReference/PostProcessBuildAttribute.html.