Terminal has tons of great applications on the Mac. By accessing the Unix underpinnings of Mac OS X, Terminal allows power users and newbies alike to do things with their Mac that may not be enabled out of the box.
Code monkeys and script jockeys frequently use Terminal to run longer processes than typical, like compiling code (the process of making all those little lines of code into an app that will run on your Mac) or running scripts. When they finish, they finish. There’s no built in way to know that they’re done.