You back load a contract for two reasons. First, it is a way to play net present value. The NPV is less than the AAV x the number of years because the out year dollars are worth less than near term dollars. Second, you backload a contract to take advantage of the way the luxury tax is calculated. The luxury tax is calculated off of AAV. If you expect to spend more in the future, you backload the contract, take the AAV hit upfront, in order to leave spending room in the out years. The only mitigating reason would be if you were concerned about cash flow, but if you are LANC and not LAC, it does not matter.
Warning - comparison to Red Sox payroll management coming up That is essentially what the REd sox did with Youkilis, Lester, and Pedroia. They have backloaded contracts. They took the AAV hit in 2009 and 2010 in order to have spending flexibility in 2011, 2012, and 2013.