Not every Privacy Permission is added manually. If you look at the example table below, you can see that many of the permissions are added automatically, and as the Privacy Permission is a custom object, we can use Salesforce automation to add it.
This is just an example and you need to determine your own Privacy Sources and Communication Rules.
Example automation
Inbound lead
On creation of a new lead with a Lead Source, you can use Process Builder Workflow to create a Privacy permission for the lead with a Privacy Source which you have agreed is for that Lead Source.
Attended conference & scanning at exhibitions
The way you track attendance and capture leads will determine how you load the leads into Salesforce. Most event apps allow you to download the leads as a CSV file. Some apps have a tight integration into Salesforce.
You might use a CSV file to import the Leads or Contacts and then their Privacy Permissions (Here is the help article on CSV imports). Alternatively, you could load the leads, and a Process Builder Workflow creates the Privacy Permission. You just need to make sure the Lead Source is populated and the Process Builder Workflow reads the Lead Source to determine the correct Privacy Source.
Exchanging business cards
Whilst this may seem 100% manual, there are business scanning apps on the Appexchange. So, when the app loads the lead, the Process Builder Workflow creates the Privacy Permission. You just need to make sure the Lead Source is populated and the Process Builder Workflow reads the Lead Source to determine the correct Privacy Source.
In sales cycle
When a new opportunity is created, or it reaches a certain status, then you can use Process Builder Workflow and Flow to create the Privacy Permission record for the Contact Role with a Privacy Source of "In sales cycle" (or your equivalent).
Signed Contract
When an opportunity changes to "Closed Won" then you can use Process Builder Workflow and Flow to create the Privacy Permission record for the Contact Role with a Privacy Source of "Signed Contract" (or your equivalent).