Whenever you record a voicetrack or add a new item via the Edit Audio window then, of course, the item has to be uploaded. In order to manage these uploads there is a background uploader which allows you to continue working in WebVT® while the uploads are done.
The Upload Queue is just a simple way to monitor the upload progress and also to cancel any pending uploads. You can access it by clicking the Upload Queue icon on the toolbar.
It uploads sequentially as opposed to everything at once and It shows the upload progress of the current item with the other waiting items underneath. If you want to cancel one of the pending items just click the red spot with the X in it. You will be prompted if you wish to do this.
When there is nothing waiting it will just say "Waiting for files..."