What good is the Scroll Lock key?

It's more of a vestige from the IBM PC Keyboard. Wikipedia has a nice history on it.

"The Straight Dope has a good summary:
http://www.straightdope.com/columns/read/2125/whats-the-scroll-lock-key-on-my-computer-for

The Scroll Lock key has appeared on the keyboards of IBM personal computers since the original 83-key PC/XT and the 84-key AT layouts, and remains on the 101-key and greater ""enhanced"" keyboards currently in use. The Scroll Lock key wasn't on the original Macintosh keyboards but appears on the Mac's ""enhanced"" keyboard.
The main intent of the Scroll Lock key was to allow scrolling of screen text up, down and presumably sideways using the arrow keys in the days before large displays and graphical scroll bars. You can see where this might have been handy in the DOS era, when screen output typically was limited to 80 characters wide by 25 rows deep. For some types of programs, spreadsheets being the obvious example, it's still handy now. In Microsoft Excel, Scroll Lock allows you to scroll a spreadsheet with the arrow keys without moving the active cell pointer from the currently highlighted cell. In Quattro Pro, another spreadsheet program, Scroll Lock works in a similar manner, although in contrast to Excel it's not possible to scroll the active cell pointer completely off the screen."

Ctrl+Scroll Lock removes annoying message "No files were found to look in. Find was stopped in progress." in Visual Studio. So 'Scroll Lock' is the best key on my keyboard.

Auto-run in World of Warcraft and many other MMOG's.

In the FreeBSD console, it stops the screen from scrolling, and allows you to page back through the buffer.