An application gets caught by a policy and this The Environment Variable action sets an environment variable that the application can use. Any application it spawns would have that same environment variable, from there additional application filters and policies could be used to catch that specific environment variable and do something about it. One example that has occurred for this action is when installers spawn multiple installers. For example, a customer creates 2 policies: one that catches the initial trusted installer and another that catches a specific environmental variable. The first policy elevates and adds a specific environment variable such as "ArelliaCatchThisVariable=TrUsT3D", then the second policy will look at all applications for that specific environment variable (this is why you never should make it something that someone would think of easily) and elevate those applications. 
Sets the Environment of a process to contain the specified Environment Variable.
To Set Environmental Variable Action
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of a process which could change the behavior of an application, or be caught by an Environment Variable filter in another policy.
After you create a new Environment Variable action you can configure the Name of the action, environment variable Name, and environment Value. The New Environment Variable Action appears in the list under Environment Variables, as shown in the following screenshot.
