Pay now and consume later: Immediate gratification can lead you to make purchases you can’t afford, or may not even truly want. Impulse buying also deprives you of the distance necessary to make reasoned decisions. It eliminates any sense of anticipation, which is a strong source of happiness. For maximum happiness, savor (maybe even prolong!) the uncertainty of deciding whether to buy, what to buy, and the time waiting for the object of your desire to arrive.
Next time Jono complains at me for spending six months agonising and analysing about a new phone or new laptop or something, I shall tell him: it is science.