If you’re operating an ecommerce webshop you’ll have data from payment provider redirects in your reports. The problem is, that Google Analytics “forgets” the last click Campaign Tracking Information and interprets that hit as if e.g. Paypal actually sent a new user to our shop. Of course that’s not true and that’s why you can add those websites to your referral exclusion list.

The setting can be found in the Property Settings under Tracking Info.