Flushing your computer's DNS cache will allow you to see the DNS changes much quicker.
For example if you are transferring a site to a new server and it feels like it is taking forever. It could be that the transfer is complete but your computer's DNS cache is not updated and as a result you can not see the change.
The old fashioned remedy is to restart you computer a few times.
Another remedy is to go into the windows command line and type in some commands.
To streamline this task and help people to avoid going into the command line I made these one click solutions.
This VBS file will flush the system DNS thoroughly (Administration Access Required):
If you don't have administration access you can try this ".bat" file to flush your computer's DNS:
You can place these files on your desktop and use them at your convenience.
For the Mac commands you can look here: