If you charge someone with a crime, you want to guarantee that they'll show up for trial and possible punishment. And the idea behind bail is that if a criminal defendant has a large amount of money on the line, he or she is more likely to appear. The accused (or a bail bondsman) puts up a percentage of the bail amount, and they get that money back when they appear for trial; skip town and you're on the hook for the full amount.
Which is all fine, in theory. But what if you can't afford the bail, or even the bail bondsman's percentage? Then you languish in jail until trial -- incarcerated even though you might be innocent. Critics of this system gained a new and perhaps unexpected ally last week: The U.S. Department of Justice. The DOJ filed a brief in a Georgia case, claiming that bail schedules that imprison poor people for not being able to afford bail are unconstitutional, and bad public policy to boot.