Addicott Web has a great little article online that goes in depth on the uses of WordPress conditional statements. The Conditional Tags can be used in your Template files to change what content is displayed and how that content is displayed on a particular page depending on what conditions that page matches. These statements enable a wide range of flexibility when it comes to when and where to display content. In fact, I use conditional tags all the time with my use of the Widget Logic plugin. I tell the widget which page I want it to be displayed on with a conditional statement and it only shows up on that page.
I love these things. Let me know in the comments what you’ve been able to achieve using them in your own theme or widgets.