I have been trying to get a handle on iCloud Family sharing before I turn it on. There are two potential issues I could see having with it. First, is iCloud storage space shared amongst the accounts or is it linked a particular Apple ID. Second how does PhotoStream work with it. My wife and I currently like sharing all our photos so we can see what the kids are up to when they with one or the other of us. Will that still be the case?
iCloud storage is not shared. Of course I realized this after upping my storage. Really this is an odd solution to use as just sharing an iCloud id between devices does the same thing AND let's you share the increased iCloud storage for backups and other things. Was hoping this would help my wife out since she hates getting my notifications and warnings every time I add a device/service or two-factor authenticate. Oh well, maybe in a future version they will refine and add features.
According to Apple's Terms and Conditions:
You can share information such as photos and videos via the Photo app, events via your Family Calendar, reminders via the Reminders app, location information via Find My Friends, and device location via Find My iPhone.
This may not be an exhaustive list.