Tip # 6: Heavy Lifting with Processing Rules
Processing rules are applied before Visitor Identification, Segmentation and Transformation Architecture (VISTA) rules and marketing channel rules. Processing rules can be used when you want to do simple pattern matching or concatenate values. You can also use them to assign variables based on query string parameters in the URL, any SiteCatalyst variables, or Context Data.
Processing rules, however, have a few limitations; fortunately, those are the ones that can be solved by a VISTA rule that runs right after the processing rule. Processing rules cannot split overloaded variables that are delimited or exclude traffic based on IP address or even move traffic from one report suite to another.
This gives you a chance to assign values to other custom traffic and conversion variables based on any logic determined by your business. So, if you are looking to assign a custom conversion variable based on multiple values in custom traffic variables or even an event, the processing rules can be used. One example of a processing rule is to determine the value of your campaign based on a URL parameter and run a few rules before assigning a value to it.