Nothing bad will happen. You may notice loading a page you have visited before will be a tiny bit slower, but it will then be cached again.

After a quick Google, I found a pretty good explanation of how it works.

By default, your computer system keeps a DNS resolver cache which stores the IP address attached to frequently used DNS names (and Internet URLs, which are essentially the same thing). This enables your system to bring up frequently accessed web pages quickly, without the need to first consult a chain of DNS servers on the Internet to find out what IP address is associated with.

Source: [ Register or Signin to view external links. ]

Flushing your DNS cache is useful if a site has recently updated and you can't see the new version for whatever reason.

If you want to get your network adaptor a new internal address on the network you can use /ipconfig release BUT remember to use /ipconfig renew or the system will not attempt to get a new one.