If you're trying to save space on a form, you'd be tempted to put the field label in as a placeholder inside the field to save space. But the system forces you to put a label in Label field. If you don't, you cant' save the form and will give a cryptic error that says "name cannot be empty". But there is no field called "Name". It should at least say "field name..." or even better "field Label..." since that's the name of the offending field.