User blog comment:Brandon Rhea/Bringing down the banhammer: Best practices for blocking/@comment-4578246-20120315210439/@comment-33628828-20120315214638

I'd say that everyone deserves a warning, except for the most obvious cross-wiki vandals and spammers. It is very hard to make a judgement about whether or not a user is acting in good faith, and you can always afford to give a warning. Best case scenario, the user learns from their mistake. Worst case, they make another bad edit and you temporarily block them. Either way, it takes very little time to revert one more edit, so I find warning to generally be the best way to go.