Exactly - the important thing is you need to actually understand the risk, and make an informed decision what level of loss is ok to you (and you should understand whether or not it's actually saving you anything - as you say, it makes sense if it is faster; there's no point losing data if you don't gain something from accepting the risk).

This is also perhaps the biggest problem with MongoDB: It's fast but unsafe "out of the box", and not everyone will know that when they use it. I think that's a large part of the problem a lot of people have with it.