What's an RRSP Loan and When Does it Make Financial Sense to get one?

An RRSP loan is just as the name suggests. It's a loan you can contract for the purpose of investing in an RRSP. Essentially, an RRSP loan allows you to get a loan in order to save for retirement. But what would drive someone to get a loan in order to save for retirement? When does it really make financial sense to get a loan for the purpose of retirement saving?