That’s a great question. Companies differ in their approaches to this. Some (like Crytek and Bungie) happily divulge detailed technical information even before the games using the techniques have shipped. Others have a policy against ever disclosing anything; most are somewhere in the middle. If your company is more on the secretive side, there are several responses. One is that the companies with the most open policies are often the most successful, so this openness doesn’t seem to be hurting them. A good compromise is to wait until the game has shipped before disclosure; then any competitors who copy the technique will be chasing your tail as you evolve improved techniques for the next game. Some companies make sure to submit patent applications before publication. I’m personally against software patents, but this does give one possible answer to the lawyers, and if you were going to patent it anyway you might was well publish it afterwards (NOTE: I’m not a lawyer and none of this is to be construed as legal advice of any kind).

Game development isn’t zero-sum; all developers make heavy use of techniques invented by others, from the most basic (shadow mapping) to the more arcane (SSAO). Publishing advanced algorithms is positive PR for the company, and helps recruit good people (smart people will want to work where other smart people are, and publication is a good way to show this).

Finally, by publishing your technique, you will get many eyes looking at it, and quite likely some of them will find flaws that you didn’t see, or think of extensions and improvements. Although nothing forces these people to inform you of these improvements, in practice after you publish most people will, often in excited conversations just after the presentation. This is another direct benefit; you can think of it as encouraging development in a direction which your company has already found useful, to your future benefit.