Campaigns are a way of separating your data and settings. Think of it as having multiple Synccentric accounts within one login. You can stay under 1 campaign...or switch back and forth between many campaigns.
When you create your account, you are automatically placed in a "Default" campaign. You can edit this campaign to edit the campaign name, the Amazon locale/marketplace, or add your Amazon MWS keys to unlock certain features and quicker searches.
The number of campaigns you can have depend on the plan you are on and range from 1 to 10. Here are some common examples of what campaigns can be used for:
For more than one locale, i.e. setting up two campaigns, one for United States (amazon.com) and one for Europe.
For multiple suppliers, i.e. each campaign would be dedicated to a specific supplier or manufacturer.
For different strategies, i.e. you may pay special attention to a specific group of products that you want to keep separate from your mass list.
For different settings, i.e. you may want to update some products more frequently than others. You could enable the 'auto-search' feature for one campaign and manually start searches on the other campaign. Another example is if you had different search settings like retrieving 'duplicate' listings for some products but other products you might just only want the best listing returned.