Since the release of OS X Lion, Safari when launched will restore any windows and tabs you may have had open when it was last quit.
Occasionally this can be a really useful feature but it can also be a laborious task to close each tab individually, especially if like me you tend to keep lots of tabs open. Here is a really simple tip that allows you to choose whether you want to restore tabs or not on an “ad hoc” basis:
When you want to open Safari without restoring tabs just hold down the shift key when launching the app from the dock.
This also works with the other Apple apps that take advantage of the OS X Auto Resume feature such as Text Edit.