There’s a lot of situations where you design or develop something with fixed width. Let me give you an example.
Say you have a form with two columns. Your left column holds a label, ”Addictive”, and your right column holds a textbox. In most of the cases you probably set a fixed width for the left column. But what if your site fetches the label text depending on what language your user has chosen? And what if the translation is a lot bigger than the original?
For instance, ”Addictive” in English is ”Beroendeframkallande” in Swedish (yup, that’s one large word, or actually 2 words put together). That will make your little label-div trying to break lines and ultimately mess up the look of your page.
Apples iProducts has a great implementation of this and an easy way to find it is to compose a new e-mail and start writing in the to-input. The longer the e-mail get, the smaller the font-size.
I ran into this little smart jQuery Plugin called Fit Text that looks very promising. Go have a look!