If I tick optimised photo storage on the mac, then I solve my space issue, I also solve the above issue of being able to access my photos at all times (albeit lower res versions which is fine.... just like iphone well a laptop is a mobile device afterall) BUT, BUT , BUT I can no longer easily retreive and backup the full res version of images that originate from my iphone, or ipad as they go direct to cloud with no easy (read automatic no clicks, icloud to timemachine transfer) of full sized images.
So now I can't just back up my photos.db file as it doesn't have all the photos anymore.