We've heard a lot about the evils of borrowing in the recent election cycle, but I don't think enough attention has been paid to the evils of not borrowing. In other words, to the problems of not having money when you need it.
Obviously, if your income goes down and you don't borrow, you can't spend as much as you used to. This is not necessarily a bad thing if you don't need to spend as much money. For us, though, it is. Accomplishing our goals will require a massive shift from personal cars to transit, and we will need to spend lots of money to develop the necessary capacity.
If your income is down and you don't borrow, you miss out on investments that could increase your income down the line. Worse, deferring maintenance can mean bigger expenses down the line, as with the Manhattan Bridge. The worst is when you spend money for infrastructure that doesn't get used for 73 years.
It may be better to borrow if it will increase your income later, if it will avoid much bigger expenses, or if it will allow you to put previous investments to use. You just need to be fairly certain that the costs won't exceed the benefits. Of course, you can never be completely sure: nothing about the future is a hundred percent certain. It's important to be careful and not take big risks. But it's also important to take small risks to avoid major expenses.