1) You will need to sign in with your Hue account even when using the app locally and
2) This will store (a copy of) all metadata in their cloud to enable you to use remote access.
Arguably this is moot if you're already using remote access but it means the Hue app and bridge will be unusuable for anyone who chose Hue because it does not store your data in the cloud. I also believe this is an attempt at consolidation to make it easier for them to support cloud-storage cameras as part of the same platform. It's still understandable why some users might object to this, especially if they have no interest in using any of the cloud features or new devices that will require it. Amazon Echo requires local access too but that doesn't mean you can opt out of Amazon storing your (meta)data in the cloud if you want to use your Echo to control Zigbee devices.