We provide the ability to create more than one campaign if you need them for segmentation purposes as some people have multiple products or brands and want to keep feedback separated. It just depends on how you'd like to view your data.
You can keep one campaign and use it continuously for as long as you'd like. Most users will run one campaign per year. On the dashboard of each campaign, you can filter your NPS score by choosing a specific date range and also filter by attributes that you've uploaded with your contacts. For example, you could see the NPS for everyone on a Bronze plan in the month of September 2015.
If you do create multiple campaigns, the total Org NPS score will appear on the right-hand side on the main campaigns page.