Discretionary Line Breaks
There are so many new features in InDesign CS3 that it's easy to lose track of some of them. One I'd like to draw your attention to is the new discretionary line break.
Like a discretionary hyphen, the discretionary line break ("DLB" from here on out) finesses where and how InDesign breaks a line of text if that line must be broken and wrapped. The difference between the two is that the former, the discretionary hyphen, breaks with a hyphen while a DLB just breaks, sans hyphen.
DLBs are useful as occasional substitutes for manual line breaks or soft returns. When you insert a manual line break with Shift+Return/Shift+Enter, you force a line of text to break and wrap to the next line. The initial effect between the two is identical. However, should your text reflow, a manual line break will not automatically roll back up; you could be left with awkward breaks in the middle or even beginning of a line. By contrast, a DLB has no effect unless it approaches the end of a line; if your text reflows such that the DLB is not close to the end of a line, the DLB-created break becomes inert again and the line doesn't break at that point.
When would you use it? Well, in episode 60 of the InDesign Secrets Podcast Anne-Marie provides a perfect example: URLs. Left to its own devices, InDesign will break a URL wherever is convenient and with a hyphen. Sticking a hyphen arbitrarily into a URL isn't the best idea because readers may not realize the hyphen isn't an intended part of the URL.
InDesign can break text awkwardly with a hyphen (above), but a discretionary line break prevents the insertion of superfluous hyphens (below).