Let' s say like this: If you need something now you ought to buy it now. But no, if you do not "need" anything now you shouldn't buy it. Because if you spent your money on something you don't need it will be wasted. So if you need money in the future times, you won't have it. As you can see its about "needs". If you want to manage your money responsibly you should spend it on important and neccessary things. Well don't ask what is neccessary that depends on people. You can fool yourself buy sayingb"I need this" but if you really don't that will be wasting.