On UNIX-derived systems it can be painful and tedious to figure out where your disk space is going. Some versions of MacOS X have had bugs that allowed log files to pile up in huge numbers; some applications have bugs that allow huge temp files to accumulate. If you're a regular UNIX command-line user you probably know how to use *du* to find big disk usage hot spots, but it's not suitable for everyone.
On a couple of occasions I have used GrandPerspective to figure out where a system's disk space was actually going, and the results can be very surprising. Here is a GrandPerspective screen shot showing my system volume:
On the right, the black area represents empty space on the volume. So it isn't near to full, but I have noticed the space used has been growing dramatically recently. With GrandPerspective you can just hover the mouse over the highlighted areas and see what files the colored areas represent. Just because a file or a group of files occupy a lot of space doesn't mean I want to get rid of them. I'm more interested in finding unexpected disk usage. So there on the lower left section, flush against the left edge of the window, that square of mostly regular-looking pale yellow blocks next to the rectangle of pale orange blocks? Those are Apple Loops -- installed with Logic Pro. I use those sometimes, and that set of files isn't growing, so I'm not interested in removing them. What about the big red blocks in the upper middle? Those are mostly disk images -- for example, Linux distribution ISO files, .dmg files for purchased software I've downloaded, and backup disk image files from Apple system software. I might want to clean out some obsolete or unused files but again, it's not really what I'm looking for. But what's that set of _huge_ orange files in the upper right?
It turns out those correspond to this directory:
You can find this great tool, GrandPerspective, here.