There are a few good reasons why you should not connect a busy web site straight to the Web:
To get better performance by caching popular pages and distributing other requests among a number of servers.
To improve security by giving the Bad Guys another stretch of defended ground to crawl over.
To give local users, protected by a firewall, access to the great Web outside, as discussed in Chapter 11.
The answer is to use a proxy server, which can be either Apache itself or a specialized product like Squid.