[mcguire]

A scenario:

You're adding a feature to your proggie. That involves modifying the main bits to add the feature and, say, adding a couple of interfaces to internal library modules.

Split out the changes to the library modules into separate commits---it's safe because nothing uses them, they're logically separate from the feature changes (although they don't appear to have a justification without the feature), the log will be marginally cleaner, and git bisect will have more granularity.

[noselasd]

Why is the staging area needed in such a case ? In more traditional systems, you'd just do, say, "svn commit library/" and then commit the rest. (and you could do just the same in git too without seeing the staging area)