In general we prefer not to remove anything at all. When we do remove something, it is usually because it fails to meet the "be nice" rule, or (in rare cases) because it is a topic that from past experience we know is about to violate the "be nice" rule (even though the original poster may have been nice).
The other thing we tend to do is to move posts if they are in the wrong forum - this is not the same as removing them.
Do you have a specific example you wish to discuss? And we might be able to give an example of why it might be removed.