Vague UI: Bad.

From Stephen Hackett's review of Evernote's new "Context" feature:

On the Mac app, the verbiage makes me think that Context can’t be turned off, just hidden. Clicking the “Manage Context Sources” button loads the Evernote web app, where sources can be turned off. These settings do sync with the iOS device, which is nice, but again, it’s unclear if this feature can be disabled completely.

This is very bad. There is a world of difference between "do/don't do" and "show/don't show". "Show/don't show" implies that the action is happening no matter what you choose. Unless you have good reason to do otherwise, it's generally better to build an app with settings that "do/don't do" instead of "show/don't show". It impacts many important things, including performance, battery life, network data usage, storage space usage, and privacy.