Does it do anything at all or it is only for documentation. If it is only for documentation, why documentation doesn't document it?
For example these are two methods from System.Array class:
[ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
public static void Copy(Array sourceArray, Array destinationArray, int length)
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
public static void ConstrainedCopy(Array sourceArray, int sourceIndex, Array destinationArray, int destinationIndex, int length)
However documentation doesn't even mention that Copy or ConstrainedCopy are decorated.