There are tons of times I want to try something locally without affecting the main repository. It hurts trying to keep uncommitted experimental changes from messing up local upstream, while still switching back to the old code to fix a bug that affects everybody. With git's local branches, rebasing, and fast branch switching, it's easy to keep your local, not-yet-ready changes in a branch, and fix bugs on master, for example.
Allowing other people to pull your changes directly from your repository for testing, without committing it, is also a big plus. "Hey, I have this fix that I want to test before I commit it. Can you pull tag omg-git-is-awesome from my machine and test it to make sure I didn't mess things up?"
Overall, DVCS just fits better with the way I work. Note, pretty much any DVCS will give you similar advantages. Git's just nice because it feels fast, and I'm just comfortable with it. Plus, stuff like rebase and bisect are sweet.
Actually browsing around I found this very useful:
short and sweet: no metadata
http://www.newartisans.com/blog_files/diving.into.git.php
http://www.simplisticcomplexity.com/2008/03/05/cleanly-migra...
You used to be able to call "git", no options, it would tell you how many commands it has. "wc" says 140!
1. I can commit things locally before committing them to the main repository. This allows me to commit something in a manner that separates it from all future changes, but test it for a few more days in future development before I actually push it to the main repository.
2. I can correct past commits. This means I don't have to clutter up the history with "fix typo"; I can just amend the previous commit. Obviously this isn't useful for stuff far back, but if I commit something and 2 minutes later someone points out a typo, I can fix it. A messy history makes development and bugfinding harder; git helps avoid it.
3. Git diff is formatted a bit more nicely than svn diff, IMO.
Watch the entire thing.
You don't.
For revision control you can use CVS, SVN or VSS if your tastes include MS. Git was born out problems with the Linus, "the Git's" attempt to adopt BitKeeper for the Linux kernel ~ http://en.wikipedia.org/wiki/BitKeeper The only reasons I can think using Git would be if you are using Rails, developing OLPC or hacking on kernels.
The rules change of course if you are an individual hacker or a new startup as more and more software uses git. Plus you can use github.