I have been in the safe and lock business for almost 18 years. I have delivered and bolted down hundreds of safes. If you have a safe weighing less than 650 lbs I recommend bolting it down! Anything over 650lbs can be at your discretion, but keep in mind if someone can get it in there than that means, someone can take it out! Bolting down a safe of any size should be done by a trained professional to make sure that it is done right. Watch a very interesting news report in Houston from abc 13 about a safe being stolen and the burglars being chased by the police at high speed across the city:

You can see from the video above why I always recommend bolting down your safe professionally!