The subscription service is just used to sync between devices, i.e. the app works completely offline once synced. You can do the same with Dropbox without a sub

The subscription service is just used to sync between devices, i.e. the app works completely offline once synced. You can do the same with Dropbox without a subscription, but in that case you'll need an app license (which you can no longer buy separately). The subscription bundles the app license + syncing, for $2.99 a month.