Tying a promotion into a holiday can be an effective way to get a customer's attention. Holidays can also provide a "reason why" for a promotion.
When an advertisement or a promotion doesn't work as planned, you just got some important information -- what didn't work.
Customers love free offers, and the word "free" helps to get their attention so they will continue to read your ad or sales letter.
The customer's (client's, patient's) initial response to a marketing message is, "I don't believe you!"