You really couldn't have just googled this one bro? Ambien tends to be wicked effective for sleep. It works fast and hard. But the biggest downside imo is that it doesn't last very long, at least not as long as the full 8 hours of sleep you're supposed to get. The CR stands for controlled release, it's to help you stay asleep for a full night's sleep. It's just like every other CR/XR/ER before it, same substance, longer duration.
"Ambien CR releases slowly over the course of the night to help you stay asleep......ambien is for people who "can't" fall asleep. Two different sleep problems."
-I just read that two seconds after posting this. I had no idea they were for two different sleep problems