When should you add garlic to cooking?

OK, I've read recently, that you should add garlic towards the end of cook time in your dishes, 3 minutes or so, because that's all the time the garlic needs to disburse it's flavor, and that way it won't kill it's nutritional value. But my mother-in-law (Who is very knowledgeable in the kitchen) says that's hoo-ha. Anyone know these facts (Or have any sites that will help?)