If you file early, and then discover you need to change something, you're stuck. Once you submit your tax return you can't do or change anything until "AFTER" the IRS has started accepted e-filed returns. Then if they reject the return you can just correct it and re-submit it.
If they accept the return, then you still have to "WAIT" until the IRS has processed your return completely, before you can file an amended return. An accepted return is not completely processed until "AFTER" you have received any refund you may be due. So filing early has the potential to put one "way" behind the curve, thus delaying any refund due for a very, very long time. Amended returns can take 6 to 12 weeks to process, and sometimes even longer.
