I assume this is a serious question. I suppose the simplest answer is: to increase your spending (ability) right now, with the expectation that after the debt

I assume this is a serious question. I suppose the simplest answer is: to increase your spending (ability) right now, with the expectation that after the debt has been paid off you will be achieve a net positive value. A small business might borrow to buy expensive equipment which will enable them to offer additional service, or to access other market segment. Along a similar line, a country might borrow to accelerate their growth (e.g. investing in infrastructure projects).