On my old 16 GB iPhone 5 iMessage was a major culprit of using up what little storage I had. Shared photo streams were another culprit. Now that I have a 64 GB iPhone 6 my storage woes on the phone are no more, and I don't have to regularly delete photos and videos from iMessage (although I should save and delete as I get them). But will the watch storage also fill up as photos appear on the watch from iMessage and Photostream? At least they are likely low resolution thumbnails, so maybe that won't be a problem.
Sean