Some producers want the session to be able to add or manipulate the original works. That's the main reason why I don't include the session unless they talking major money. And even then, I would still do any changes, and include it in writing. Other producers want to be able to run the session through something like Nuendo and change all the instrument sounds to some real nice sounding VST's, changing the whole beat prospective. Ever heard your Reason beat with top notch instruments?? Love it. but anyways, yeah, some prod. want to have full production power, especially when they dropping $120K on production.