One "trick" I've seen mentioned if you don't want to pay your first estimated tax payment by April 15th is to overpay your 2020 taxes and apply the overpayment to your 2021 taxes when you file by May 17th.
What difference does it make? Do you just avoid penalties or do you get extra tax deductions?
Correct, it would be about avoiding penalties while waiting a little longer to pay. If you rely on safe harbors to avoid penalties you might not know how much to pay until you file your 2020 taxes. Usually the estimated tax deadline and the tax filing/payment deadline are the same, so it doesn't matter, but this year they're not, so this is a way around that.