You can also defrost in the sink. Put what it is you need thawin’ in the sink and run COLD water on it until it is smushy. This is much faster than over night (which turns into three days for me, I don’t know about you), and safer than leaving it on the counter.
In the fridge I think the rule is supposed to be one day per pound.
In the sink, you can either run cold water over it or let it sit in a bowl of cold water that you change every 25 minutes.
But the reason is bacteria. Especially if “they” are a cookbook, they don’t want you to get sick, blame the food, and tell everyone not to buy their book.