When adding a related list record, I think the field that relates the module should be automatically filled in based on what the value is in the current CRM record. I have a Creator related list in the Deals module and I have it related by the Deal ID. Usually the items in the related list are created automatically and the Deal ID is filled in, but if users need to manually add a related record, it would be easiest to click the add button on the related list. As of right now that add button is useless because they wouldn't know the Deal ID, and a record created wouldn't be tied back to the deal it was created from.

Right now I'm having to create a custom button (on the view page of the deal that opens the form in a popup with openURL() and pass the Deal ID as a url parameter, while this works, the users will still forget and instead press the add button on the related list which won't actually relate the related record to the current deal, breaking the business process unknowingly.