From the IRS perspective, it doesn’t matter how early you file your return, as long as you meet the original or extended deadline (April 18, 2017 for TY 2016).
From your side, however, it’s better to file early.
For starters, the longer you wait to file, the harder it is to remember which tax deductible expenses you had throughout the year. If you didn’t keep adequate records of all your expenses, it’s can be difficult to remember what happened over a year ago.
If the government owes you money, you might as well get it as soon as you can so you have more time to make good use of it. That extra money could help pay off a credit card bill so you don’t have to continue to pay interest on the outstanding amount.
In the case you owe money to the IRS, filing your return early is still a good idea because you have until the filing deadline to pay the amount due. That also gives you more time to plan for that payment so you don’t end up owing late penalties and interest.
Filing early also lessons the odds of tax fraud. The quicker you file your return with the IRS, the less time a criminal has to file a fake tax return in your name.