You will have to pay back the debt amount anyways. The author is just saying that you get a margin of 45 days. It is useful in the cases if you are expecting funds in the near future and it is imperative for you to make a purchase before you have those funds. In such a case you can use a Credit Card.
There are always good things and bad things associated with everything. Nothing is good or bad in absolute. Credit Cards are good if you identify your spending limits and spend in those limits.
The author is just asking you to be prudent while making a purchase through a Credit Card.
