"We're booked until the end of the year" sounds suspiciously like "We're not charging enough money."
Charging more money doesn't create more time, especially if you're already solidly booked. Now it's great to quote a really high rate when you're totally booked because there is almost no risk but then it can be challenge when the client then accepts it.
I believe his point is you shouldn't find yourself in that situation in the first place.