Sorry. None the wiser. Is there a link that explains the use of the sandbox.
Also interested to know if Webrep flashes up a warning ala WOT if you click through to a Red site. That is, do I only get a warning about a bad-site from the icon in the address bar OR can I remove the icon because it will stop me visiting bad sites.
Are you using the Beta? There isn't alot written on the autosandbox yet, couldn't say much either as I'm not testing the Beta. Avast!'s original on-demand sandbox works by creating a sandboxed copy of programs that are already installed on your PC. It is made primarily for browsers, but you can try out other things if it suits you. The best link I could give you for sandbox documentation would be to your own Avast! help file.
WebRep as of right now has no site blocking that I am aware of. Since it is a built-in Avast! feature, it leaves that to the Network Shield. So yes, hiding it will not result in any loss of protection. If you look closely, WebRep never asks you how safe-or-unsafe a site is, only how much you like it and what kind of content it has.