@friendfiend if your appication is competitive then hopefully the ED will give you a lock on an early acceptance - but if each year about 1/3 of your school’s early applicants gets in eventually then you are already facing enviable odds even w/o the ED. 
Sorry I didn’t ask this earlier but what % of your school’s acceptances actually attend UChicago? If, for instance, only two of those five commit every year, then including the ED acceptance will raise the yield from your school - something that every regional counsellor wants to happen. That’s a very specific way that ED can help you.