Scanning your hard drive periodically is a good way of knowing how much space files are taking and deciding on what to keep and what to trash.
Baseline combines tools to scan your disk with features to act upon cumbersome files. We've found the program to scan a disk fairly quickly, although that can also depend on the size of your hard drive and what files you've got stored up.
We quite liked being able to save baselines, comparing in time what has been added and removed. Leopard users will probably be unimpressed though as they can do exactly the same thing with Time Machine.
After scanning your hard disk you can act upon those bothersome files. Depending on your needs, Baseline lets you compress, archive or delete these.
Those functions are directly accessible from the interface, sparring your the burden of having to open up a separate application.
Baseline not only lets you scan your hard disk from cumbersome files, but also allows you to act upon these.