If they borrow to build infrastructure, or to pay for defence for instance that stimulates the economy and creates growth which is a good thing. If they spend it on education or health that is also a good thing because a healthy and educated population is desirable for its own sake but will also eventually create growth. If they borrow to spend too much on welfare of simply to pay interest on money they have already borrowed (look it up it will make your eyes water) then this is a drag on the economy and on growth. This where we are now. Although governments worldwide are borrowing more than ever, Investors are demanding a higher rate of return to lend to the UK. As has happened before, this can lead to a debt spiral where financing the program of government becomes unaffordable and you end up with a financial crisis and austerity is forced upon you. And that's real austerity, not the kind that George Osbourne inflicted on us, real terms cuts in expenditure right across government, existing pensions and public sector wages being cut for instance. The EU forced this on Greece a few years ago which anyone can look up if they're interested. It won't be pretty.