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 two static methods of System.Array:
[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)
Their generated MSDN documentation doesn’t even mention that Copy or ConstrainedCopy are annotated.
I believe they’re used for constrained execution regions too, so the CLR knows what it can do safely. There are certain things that your code can’t do within the CER, and in return the CLR guarantees that certain out-of-band exceptions aren’t thrown.
MSDN has some more details.