I've only had X-marking for CA1 and Y-marking for CA3 and would recommend it for all subjects but the CT's. With most of the CT's you can easily mark your scripts yourself. This becomes more difficult with the later subjects where it is easy to be subjective when marking your own script. On the other hand, if your company pays, why not? I found X-marking useful for pacing myself throughout the session by sticking to recommended due dates. The actual comments by the markers may help you to a certain extent, but marking will force you to do the assignments under exam conditions (I think this is a must!) and I think this is where it adds the most value.
