After a few years, it's probably safe to say that the old inactive Campaigns in Salesforce are not influencing behavior and no longer necessary to keep. Deleting inactive Campaigns that are far older than your buying cycle will free up valuable storage space.
NOTE: Campaign Members that are directly deleted (without targeting their Campaigns) are not available in the recycling bin.
Recycle old Campaigns automatically with Storage Helper.
To Delete Old Campaigns with Storage Helper:
On the Storage Recycle Jobs Page, Click New Storage Recycle Job in the upper right corner.
Name the Storage Recycle Job (Old Inactive Campaigns).
Notes is a good place to document your criteria: Campaigns that are older than 2 years and are inactive
Create filter criteria.
Field: End Date
Logic: Less Than
Condition: Last Number of Years, 2
Save the criteria.
Select Backup Mode
Select whether you would like to Activate the job, or Keep Inactive (Please Note: To prevent important data from being deleted accidentally, we recommend keeping the Storage Recycle Job inactive until the deletion criterion is fully defined).
On the Storage Recycle Jobs Tab, you can preview records, change filter criteria, edit, delete or activate your job in the Detail Tab on the right. In the Backup tab, you can view the .csv files that were created.