Well, for starters, you will be able to leave comments on articles and individual programs. You'll also be able to rate programs, suggest corrections, use the on-site chatting interface, get recommendations on software, and probably do something else I've forgotten about.
The guest account that the Software Informer client creates for you, whilst able to do all of the above, has one significant disadvantage: you lose it every time you reinstall the client, and you have to start everything anew.
