I have a similar question, still looking for answers. I want to sync only certain folders from the photo app to my MBA. I don't want to pay for more iCloud storage. I also don't want to use iCloud Photo Library as my main source to all of my photos in my iMac.
From what I have read so far, we have no choice but to enable the iCloud Photo Library to have photos on different Apple devices. My problem is, if that is the case, my iPhone 5S and iPad Mini does not have hard drive big enough to accept all of my photos in my Photos app.