Hello garpts,
Before I answer that let me put in here the advice I give to anyone who is about to book a cruise. I've written this so many times I'm just pasting it here:
Be absolutely certain to ask your travel agent BEFORE you book, if they honor price drops. Not all do. (Also remember some sale prices, usually those after final payment, are labeled by the cruise line, as being for new bookings only. The TA cannot give you those price drops after a booking is made, it's not their decision to make.)
Also ask if they charge a cancelation penalty of their own. (All cruise lines charge cancelation penalties, if you cancel after final payment. But some travel agents charge a penalty of their own, for cancelation at any time. This can be as much as seventy-five dollars per person.
If the TA won't honor price drops, or charges their own cancelation fee, find a new TA.
OK, assuming you follow that bit of advice, there is very little advantage to waiting to make a booking. If you know what you want, you should go ahead and book it as soon as possible. ....Because:
Frequently the early prices really are cheaper. And it is more common for the price to go up as the date gets closer.
If the price drops after you book, in most cases you will get the lower price anyway.
If the price goes up, you will still only have to pay the lower price at which you booked.
The earlier you book, the better the cabin selection. If you really study the deck plans, you will see on most ships there are some really prime cabin locations that will book up first. Also, in each catagory of cabin (inside, outside, verandah) there are several levels of price, for essentially the same cabin features, usually charging more to merely be one floor up, or a bit closer to the midship. If you wait you could end up paying hundreds more for an identical cabin, because all the less expensive ones in that catagory are booked already.
Also, these days it seems that most ships are sailing at full capacity. Wait too long, and you won't get any cabin at all.
The only time booking late is a good thing, are the times that really aren't a matter of waiting. IF you can cruise with only a little notice, meaning you don't need lots of notice at work, and you don't have to book airfare to get there, then there are always some great last minute deals out, provided you're not picky about cabin choice.
In any case, I always tell people that the best way to get a deal on a cruise is to "book the deal that is out there." Meaning look to see what is out there at a great price and book whatever that is. Meaning you cruise, when, and where, and on which ship, and from whichever port and in whichever cabin level is featured in the deal.
But if you must sail during a particular week, and you have your heart set on a particular ship, going on a particular itinerary, and you will only book a certain level or location of cabin, then you will have far less likelihood of getting the deal. In that situation the only leverage you have for getting that at a deal price is the early booking.
Good luck with it.