For the most part, the concept of cruise "sales" is nothing but a gimick to get you to put down that deposit. There are some deals here, but they are limited to certain lines, etc. It's not unlike the other sales other lines offer at regular basis, one of those on the list was just offered a couple weeks ago by the line for example.
Cruising it not like buying a TV or a plane ticket. In most cases, if the price drops after you book the cruise, you will pay the lower price (if you or your TA stay on top of it). You don't need to wait for a sale to book, just find a price you like, book it, and if the price drops take advantage of the drop, if it doesn't, you booked a price you liked anyways.
If you wait too long to save the $100 or so the cabin class you want may not be available, or the cruise may sell out.