So Brittany and I have recently been cleaning up our data situation. For a while we had data spread between our MacBooks, Mac mini, iPhones, iPads, external hard drives, iCloud, etc, etc, etc. We didn't have what you would call a clear strategy... I decided to really start working on the best way to manage our data, and we are making progress. Part of that process was to get Brittany's MacBook Air under control. She had it so full of data that she was getting a warning message anytime she did anything that she was out of space. So we decided that we needed to completely start new on her MacBook. So I formatted it, but I still had one problem. Her Photos Library was bigger than her hard drive. So naturally... more trouble...
Photos provides an option to Optimize Mac Storage in Photos Preferences. One of the options has the description, "Store full-resolution photos and videos in iCloud. Originals will also be stored on this Mac if you have enough storage space". Photos will continue to download the full resolution images from your photo library until your storage space hits a certain threshold (I don't know what the threshold is, and apparently that's still up for debate....) and then stops. I decided to create a 10gb partition, and I created her library on it. Photos should download the high resolution photos until it reaches the designated threshold on the new partition. So instead of completely filling the main partition with photos (which can create problems when you want to move large data onto the drive, etc.), you now only fill that partition.
So far this has worked really well. I have noticed that the photo-analysis process seems to be taking A LOT longer than it originally did to scan the photos. We are talking it takes days to go through a few hundred photos (which was not the case before). I don't know if this is due to Sierra reprioritizing the process or if this is because of the partition. I am going to assume it is Sierra being more efficient, but I can't be certain. We are just plugging it up every night and letting it do its thing. One day it'll finish... one day...
Over all it seems to be working really well, and I'm going to be implementing this same thing on our desktop setup. We both have our libraries on there, and I plan to limit those to 5gb for each user. That way we aren't fighting for space on that machine. We will still be able to work with images if we need them, but we'll just have to pull it off the cloud.
I'm working on a tutorial on how to do this and will update this post with a link to it.