What is the best practice for using the custom Process ID attribute?
The "Process ID", that can be found under "More Attributes" in BPMN 2.0 Diagrams, are only needed when you reference to an external Business Process Management Software. In general are all attributes, that are listed under "More Attributes" only relevant for the technical execution of the BPMN 2.0 diagram. Therefore the best practice is to ignore these attributes.
KBA , BPI-SIG-PM-MOD-EDT , Graphical Editor for SAP Signavio Process Manager , How To