The event website is what any person who lands on your website can see but they will not have access to the attendees networking area so they will not be able to connect with other attendees.
As explained on the “How can I edit the modules shown on my event website and private event networking area?” post, you can choose what visitors will see and delegates too.
For instance, some event organisers leave media (videos) visible to everyone, some use the media module to allow only registered delegates to download some materials.