I have migrated from iPhoto to OSX Photos. All my Events are there with all their photos. Back in iPhoto I had Albums and Events with Events always the master. I could delete a photo from Albums and it would stay in Events. That was fine. What are the rules for Photos pls? I can see the same photos in both Events and Albums but when I search for a photo (that I know is in both places) it shows up only in Events. I delete a photo from Events and it stays in Albums. Any clues pls?
Events are now just albums. So, you can remove specific photos from Albums or "Events" without deleting the photo. Only if you delete a photo from the main Photos view is it actually deleted (and then, under File: Show Recently Deleted, you can recover it for 30 days).
I recommend deleting events that are no longer useful, as the Photos view now nicely converts into years and locations as you zoom out, which you might previously have manually set up as events.