Borrowing out of necessity or opportunity

In his book “Borrow Smart Retire Rich” Todd Ballenger discusses the concept of borrowing money out of opportunity versus necessity and at the same time does a nice job of describing financial arbitrage:

Most of us have borrowed out of necessity for houses, cars, or other purchases.  Let’s say you borrow money from a local bank for your house at 7%, the same bank where you deposit your pay check each month.  When you make a deposit to your checking account, you loan the use and control of your money to the bank for a little interst, say 2%.  The bank as a professinoal creditor lends the use and control of their money back to you at 7%.  The bank earnes a 5% spread lending your money back to you.  You borrowed out of necessity, while the bank provided a loan based on opportunity.