All sketches created by the signed in user are authorial - see the previous answer for 'authorial'.
Also if you want to use Premium Subscription, you have to sign in, because a subscription is connected to your user account.
It depends on the Clarisketch version.
From the version 1.1 you can remove the share authorial sketches yourself directly in the application, or on the server on the page "My Sketches".
In the application: Select one or more shared sketches in the gallery. The shared sketches are marked by the cloud symbol .
If you select at least one shared sketch then you'll see the following button in the top right corner: . Tap the button to delete the selected shared sketches from server.
On the server: Login to the server and go to the "My Sketches" page. There you can remove sketches one by one.
If you use an older version of Clarisketch, then send a link to your sketch to firstname.lastname@example.org and we will remove it.
Clarisketch was designed for the following main purpose: to allow you create quickly a clarification rich message, consisting of picture, drawing and a voice comment. Then to send this message quickly to some friend, colleague, family member etc. So it doesn't compete to some presenting applications such is PowerPoint or Prezi or some video editors. It's more messaging application than an application for creating a nice and polished presentations or videos. That's a reason why Clarisketch does not produce video, because creating and uploading of video is time consuming process. Clarisketch produces a special small data file, which can be sent to server quickly.
Anyway, we understand that in some cases is useful to export sketch as a video file. So we plan to add an export to video to some next version of Clarisketch
Free version: One page, up to 2 minutes of voice comments.
Premium version: Up to 30 pages, each can contain up to 1 hour of voice comments.