Making an Evernote note is great with do. I don't have to launch the app and risk switching context. Same with Todoist, Salesforce chatter, and more. The idea of one way UX (not just react-style unidirectional dataflow) where the user has a view for just data entry or retrieval is a powerful one.
I use it to email notes to myself. This recipe is one of the top killer features of my Apple Watch, as it means I always have a GTD input device available within about ten seconds.