Processing rules simplify data collection and manage content as it is sent to reporting. Processing rules help simplify interaction with IT groups and Web developers by providing an interface to:
Administrators have rights to use processing rules by default. Administrators can also grant these rights to non-administrators through the Admin Tools interface. For instructions, see 
Because processing rules permanently affect Analytics data, Adobe strongly recommends that processing rules administrators receive certification training in Adobe Analytics, and be familiar with all sources of data for your report suites (standard web sites, mobile sites, mobile apps, Data Insertion API, and so on). Knowledge of the context data variables and standard variables populated in various platforms will help prevent accidental deletion or alteration of data.
Context data variables are a type of variable that are available only to processing rules. To use context data variables, key/value data pairs are sent in by your implementation, and processing rules are used to capture these values in standard Analytics variables. This frees programmers from understanding exactly which prop and/or eVar should contain which value.
See Context Data Variables in Implementation Help.
Processing rules can monitor incoming values to transform common typos and set events based on reported data. Props can be copied to eVars. Values can be concatenated for reports, and events can be set.
Once context data variables are defined within your implementation, they must be copied to variables such as eVars to be used in reporting.