With the web viewer you can view the design with any browser on nearly any computer connected to the internet. No installtion of any software or plugin is required. You will be able to see the layout, but it is not possible to download the design. The link to view the design can be shared to your friends. So it is a good way to share a designs and avoid illegal copies of it. With the cloud interface you have a detailed control on who can see the design.
A design can be uploaded with the feature Utilities/Cloud/Share Design with Friends. This will open the web interface of the cloud and alows to prepare links to share the design. Any uploaded file will be store for 30 days in the cloud and can be deleted any time before.