It's often (or, was in prior years/decades) done to get over the standard deduction amount - more so with property taxes.  In Ca, property taxes are due twice a year,  BUT you can pay three installments in one year (then only one in the following year).

It could also be done with State estimated tax payments...pay the 1.15 one by 12.31 to move the deduction into the year wanted.  

Year one - over the standard deduction so itemize.  Following year, standard deduction.

The large standard deduction, plus SALT eliminated this strategy.

It's not an IRS *code* other than the concept of cash basis.  You deduct 'it' when you pay (or donate) it.