Hi All,
Whats the difference between putting the RG on the Operation as a Scheduling Requirement (Mandatory) and then also putting in Operation under the Resource Group?
The Resource Group(s) listed in the Operation Details are used for scheduling the job operation. Every operation needs at least one schedule-able detail. It doesn’t necessarily need to be a Resource Group, it can also be a specific Resource.
The Operation specified in the Resource Group is the Operation that gets added to the Job/Quote/Method if you drag the Resource Group from the Engineering → Resource Groups tab, onto the Operations node.
If you don’t provide that Operation, you can’t drag/drop that Resource Group when building your method.
I have personally never used this feature, I just discovered it when trying to answer this question. 
The Epicor Field Help does give a pretty good explanation.
“Specifies the default operation associated with this resource group. When this resource group is added to a method of manufacture (routing) during Job Entry, Quote Entry, or in the Engineering Workbench, this operation is the one used to create the operation sequence.”