I get why, as a dev, you want git commit -m'Fixed bug' but as the debugger guy, the reviewer gui, anyone who reads the code, that's a horrible thing to do to those readers.
Who, if you wait long enough, will be you. And I'll laugh my ass off at all the lazy committers who really could use more breadcrumbs when they have to debug their code later. Been there, done that, I haven't worked with people that lazy in decades.
edit: since HN won't let me extend the thread, let me reply to the comment below because BK does do something special.
The GUI for checkins presents you with a list of files, a place to type comments, and a big pane that shows the diffs. You type in comments for the first file, go to the next, type in comments (yes, there is a way to say use the previous comments). As you move from file to file, the bottom pane shows the diffs for that file so you can see what changed in that file.
The special sauce, that Git most definitely does not have, is when you get to the last file, which in BK is the ChangeSet file, this is where you would type the commit message. What are the diffs? There aren't any so we stuff all the comments you just typed on individual files. What does that do? Well, on the files you are usually typing in details of how you did this or that, when you get to all of those comments, you naturally uplevel and type in why you were doing all that.
It dramatically increases the usefulness of commit messages. That's why Intel pretty much mandated the use of the gui checkin vs the command line checkin.