There is a common theme in personal finance: Instead of buying expensive [whatever], buy the cheaper [whatever] and invest the difference.
MasterPo is all for buying on the bargain and certainly in favor of banking or investing the extra for the future. But there is another factor to be considered: Reality.
It takes a lot of personal discipline to be able to actually save/invest the difference between the expensive thing and the cheaper thing. And to exercise that discipline month after month or even just year after year. The temptation to spend the savings is great. And the reality is that things happen in life that can get you to say you'll spend the savings on something else instead of investing it.
On paper buying on the cheap and investing the difference sounds great. But functionally to implement such a plan over the long haul is a whole other story that usually doesn't turn out to a happy ending.