There is only one thing I modded in this thread: I removed the "exotic" tag for all the animals in-game.
Facts
Cave crocs hatch 20 to 60 eggs at a time (average number: 40). This number of eggs is the second best in the game (saltwater crocodiles are the winners). The crocodiles hatchlings grow to full size in two years. Their meat has a value multiplier of 4(!). A full grown cave croc can produce up to 50 (or something like that) units of meat and forty in average. So, if we do the math, knowing that a breeding pair will hatch eggs two times a year in the best condition and that in average there will be 40 crocs with 40 units of meat each, we get 3200 units of meat a year, enough to feed 200 dorfs for two year. So, once you start farming them, after two years you will have a fully operational meat farm, capable of feeding a fully sized fortress for the eternity.
Why should I choose them over crops?
1) You will need less crops for feeding your dorfs and will have more to make booze, making exotic booze farms much easier to create.
2) You can cook meat without risking your industry (as cooked crops don't leave seeds behind).
3) You can use cave crocs for more uses. Because of their enormous value, they make marvelous animals for zoos. They can be used to have a super bone farm, and, above anything else, they can be used as a last stand defense against enemies.
4) Who's more badass: a little dwarf farming putting seeds in soil for his whole life, or a dwarf who's breeding cave crocs?
Why should I use them over saltwater crocodiles?
The meat of the cave crocs is more valuable than the meat of the saltwater crocs and cave crocs can be found on every biome.
What am I waiting for?
I don't know. You should be farming them RIGHT NOW.