Some disclaimers: I own a Mac since 2013. I owned an iPhone 4 which I eventually switched to a Samsung Galaxy S3 (mostly because of screen size) until they released the iPhone 6, I now own an Iphone 6s. I am not hardcore Mac fan, I simply enjoy the hardware. It just works (most of the time).
However, when it comes to its software eco-system, I hardly use them. The only iCloud feature I really like and have proven useful is the "Find my iPhone". I sync my contacts with gmail, an although I use Notes and other iCloud software just a bit, I normally rely on third party software (Google, Dropbox and the like). I like to keep my self as OS agnostic as possible.
But photos and an online backup is an issue. No other app is allowed to continuously sync the photos automatically, at least not natively. Dropbox and other cloud syncing app relies on the location feature of iOS, so it's a bit of a trick:
Notes on background uploading
Normally, camera uploads only runs while the Dropbox app is open and for a few minutes after you close it. This is due to a limitation in iOS. However, if you turn on background uploading, the app will automatically resume uploads whenever it detects a significant change in your iPhone's location.
Note: This feature is designed to make camera uploads work more efficiently; it does not collect your location information in any way
When the background uploading option is set to On, you'll see the location services arrow appear at the top of the screen:
Not only that, it doesn't (till now at least), sync the live photos (moving photos) of iPhone. So I ended up, for the sake of backup, buying iCloud storage just for the photos and videos. I then enabled the seemingly nice feature of Optimize iPhone Storage and get on with my life.
So far so good.
At some point, I needed to hard-reset the iPhone (I still do, haven't done it yet), but I knew that it would download all of my photos and videos, or at least its thumbnails, all over again. The optimise storage only keep the full version of recent photos and download the rest. I guess this is not an issue for the US, but here, broadband internet is not that good, I normally am on a 6mb download/1mb upload line. So I simply wanted to upload the photos somewhere else, and start fresh. To do that I configured iCloud Photo Library on my mac, free enough space for it, and wait until everything downloads. Exporting the photos from the OSX Photos App creates both JPG and MOV files for the live photo, so with that I could simply arrange the files as I want on my Dropbox and upload them (again) to the cloud. At least with dropbox I can actually save space by not having them on my drive.
So i see how overtime, the iCloud Library becomes a mess. You can only have it all sync, or not at all. And if you have the "Optimize space" enabled on either device, you would have to eventually download files over and over again.
I am now doing all this to reset my iphone. I want to start with an empty photos library, so once I finish uploading everything to dropbox, I will remove them to start fresh. From there on, I will disable the "Optimize storage" feature so that I will always be able to download photos from the iPhone to my computer without having the iCloud Photos Library enabled on it or needing to download anything. And will only keep on paying the storage for backup sake, but when it becomes full (either the phone or the storage) I will move them to Dropbox and keep the iCloud Photos Library as small as possible.
UPDATE: It turns out, that even after you Download all of your Originals as per Photos settings, when you attempt to export files, mostly videos still needs to be downloaded. This is an even bigger inconvenience. I want my files!