There was a post I found a while back on the official Cyanogemod site that went into details about Nightlies, Milestones, Release Candidates, and Stable Releases. What would be most important for users of CM11 at this time which was explained in the post is that you either stick with updating from nightly to nightly OR milestone to milestone. If you're on a nightly and you update to a milestone snapshot, you risk damaging and messing up the OS. Vice-versa as well and should also apply to RCs and Stables. Nightlies are bleeding edge and have the latest code while a milestone snapshot is more stable, but has older cold. So going from nightly to milestone snapshot would be one heck of a messy downgrade.
srry for dis messy post btw qq