When the Execute as master process option is enabled, the command line application will be executed on the master machine of a job node or grid setup. Export, import and post-processing steps are still run on the execution environment selected by the user when launching the external application. This setting has no effect for single server setups, where all execution happens on the same system.
With this option unselected, all stages of the external application are run on the execution environment selected when launching the external application. This is the default situation.
Execute as master process is not recommended for use with memory or cpu intensive tasks as the command line application will be launched on the master system without consideration of how busy that system is, or what processing capabilities it has.
For grid setups: Whether or not the Execute as master process option is enabled, export, import and post-processing steps will be run on a grid node if a grid execution environment is selected when launching an external application. This is why the Working directory option must be set to Shared temp-dir when running an external application on a grid setup.