The issue is if you take a lot of photos that you will want to upgrade. But it is a small amount.
Various features like "auto install apps I installed on other devices" want to hide this away, but they fail. For example, they will install apps I installed on another device, but they won't install them in the same position on the screen (something very important for me), and they won't delete it.
Also many apps, including apps made by Apple, do not use iCloud to store their settings and data, or use it inconsistently (e.g. only for data, but not for settings). One spectacular example is the messaging app, which doesn't show SMSs received on all devices (although it shows SMSs received on other devices before I made the backup, making it even more confusing). Of course, the messaging app shows iMessages. So some messages work, but others don't.
http://www.apple.com/pt/pr/library/2014/09/02Apple-Media-Adv...
Whilst there was a security issue in iCloud it wasn't the root cause behind the "fappening" scandal. It was purely social engineering.
I still haven't fully bought into the Google ecosystem but I'm slowly move over.