When you flash the NDC tar with Odin it will wipe everything and you will have to reinstall Philz, re-root the phone, etc. You can flash whatever you want after you're finished.
If you plan on switching back to CM11 or another AOSP rom I wouldn't bother. I've seen several reports on XDA of the NDC and ND8 bootloader having a bug to where you can't charge the phone while it's off. Like if you run the battery dead. This only affects AOSP roms so if you want to run Touchwiz, or don't care then it's not a problem.
I still haven't updated to NDC so I'm just passing this info along. I see no need to, I'm running AOKP right now and plan on trying CM11 again whenever the new snapshot is released.