In theory, iCloud is a really good solution. It is glitchy and sometimes slow to sync and the Photos app is very poorly integrated for use with other apps on the Mac (works much better in iOS). I have my entire 35,000+ library in iCloud with the original full-sized files uploaded and with optimized -for-size complete libraries on my Mac and iPhone. The 150GB library and my extensive hierarchical folder and album structure take up only 7GB on my phone. It's a neat system and will be great if/when they work out the many little annoyances and errors.