Stops all data collection for a user going forward. block also erases any data previously associated with that user, including all of their attribute and analytics data. The block will take effect as soon as the “success” response is returned. It may take up to 15 days to delete the user’s data completely.

Note that the block call deletes a user's past data, but does not delete the user entirely. This allows you to use the unblock call to resume data collection.