So far, my move from Aperture to Photos has been mostly good. The new Photos app is a good fit for me. I don't do much professional editing, and I like having all of my photos available everywhere.
The only bumps I've experienced so far were related to the initial import from Aperture to Photos and the initial upload to iCloud Photo Library. I'm posting these anecdotes here in case it helps someone else. . . because as of the time I'm writing this, I did not find a lot of insight elsewhere online.
The initial upload was confusing (to me at least)
I don't have nearly as big of a photo library as a lot of people. I only have just over 10,000 photos and a little over 100 videos in my current iCloud Photo Library. I have a reasonably fast upload speed though my cable ISP (over 4 Mbps up), and online backups like Backblaze and Dropbox have always performed faster than I expected.
Even though I paused or turned off other online backup services during the initial iCloud Photo Library upload, it took much longer than I expected—approximately one week.
In the final days, I was able to speed up things by leaving my MacBook Pro awake and open as much as possible and also making sure the Photos app was open. Just based on my observations of network traffic, the iCloud upload services seemed to run faster when I did this.
The biggest point of confusion for me, however, was the iCloud Photo Library sync behavior during the initial upload. Shortly after I initiated the upload on my Mac, I activated iCloud Photo Library on my iPhone as well. The iPhone upload time was negligible (presumably because those photos were already in the cloud), but it surprised me when I did not see recently taken iPhone photos on my Mac.
Photos taken on my iPhone did not sync to my Mac at all until the Mac's initial week-long upload finished. In the weeks since it has finished, however, everything has been syncing just fine, and I've had no syncing issues at all. None.
But as the heading above says, the initial part was just plain confusing and unexpected. The fact that the photos were not syncing days after my Mac and iPhone were both connected to iCloud Photo Library did not inspire confidence, but I'm good now.
Local photo library sizes don't make much sense to me anymore
At some point during the initial upload to iCloud Photo Library, my Mac decided that it no longer had enough disk space locally for my photos (even though my local disk was the original source of all these photos. Hmmm. Yeah.).
This optimization setting seems to work extremely well on my 64 GB iPhone. I was initially concerned that by activating iCloud Photo Library on my iPhone, it would gobble up storage, but that hasn't happened at all. I have tons of free space despite having access to all of my iCloud-based photos now.
Because this seemed to work so well on my iPhone, I didn't have a major problem allowing the same optimization black box to run wild and free on my MacBook Pro, where I'm constantly running out of disk space anyway.
And so everything finished, and everything seemed fine until. . .
I recently noticed that my local Pictures folder (home of the photo library files) had ballooned in size to over 85 GB, and I was once again running out of disk space. This made no sense to me because the space occupied by my photos and videos in iCloud was only about 55 GB.
And so—I'm guessing—not unlike ancient agriculturists at the mercy of the heavens, I raised a fist to the cloud, albeit while cursing about very different problems than they ever did.