It sounds like it might be a useful program for any complicated project, even if the project isn't a program.
As a programmer, I am tempted to say "unless the project is actually a large program". "Large" is relative, of course.
Of course, I have seen LightTable before the comment on LW, and I tried to imagine applying it to any basically data-crunching (as oppposed to mostly UI) program. Visualising computation may look like a good idea. Unfortunately, at the level it is demonstrated in the demo, it is simple enough for anyone who even tries to write a big program to keep it in mind.
When you have multiple layers of abstraction and each of them...
If it's worth saying, but not worth its own post, even in Discussion, it goes here.