I think it's dangerous any time you spend money before it's in your hand. You never know what's going to happen.
That's the sweet spot. Then you know you had your money all throughout the year and weren't giving Uncle Sam an interest-free loan.
Because of the way this form used to work, it calculated the tax as if you had received the money over a five-year period. You would divide it into five equal parts and pay taxes on each of those parts which significantly reduced your tax bill.
If you want to save tax dollars, deferring your funds into a retirement account is probably the best solution. That money grows tax free and (if you take out a traditional IRA) you reduce your taxable income in the year you make the contribution.