I think if the user thinks they are suddenly being tied to a service may push them away. The services that use the 'save my info for later' technique are most

I think if the user thinks they are suddenly being tied to a service may push them away. The services that use the 'save my info for later' technique are most likely seen as easier because it is similar to how you use your local computer. You don't have an 'account' on your laptop. (Well, technically you do, but most people just believe that is just a password) You simply save something in your documents for later. By making the user believe that they aren't tied to anything, but just saving data for later, you can make them more likely to store their data on your servers.