A prime example was when I subscribed to NYTimes, and a few months later wanted to cancel. The only way to cancel was to make a phone call, navigate a phone tree, and wait for an agent. That was absurd, not only because I'm international and find it less convenient to call a US number... but particularly because I signed up and created the subscription online. NYT knew what they were doing by making it difficult for people to cancel.
With PayPal in between, I was able to easily just terminate the agreement. NYT could no longer suck money out of my card.
NYT has since upgraded to allow managing your subscription online, including upgrade/downgrade/cancellation.