DataTweet knows you only as a Twitter user (there are no separate DataTweet accounts). So, signing in to DataTweet consists of authorizing (or reauthorizing) DataTweet to access your Twitter acount. If you specify "Keep Logged In", you won't need to repeat this step (at least from the same browser and the same computer)

Authorize DataTweet to post on your behalf.

Keep me logged in.