One thing I hate about Android phones these days are the opt-out sync features. All my data is synced to a magical location, and once synced they can never be erased. If you make a single mistake, then all your data has been essentially stolen.

For example, I created a 'Samsung account' to try out the heart rate monitor on S5. I didn't know that if I create an account like that, the phone instantly uploads (syncs) my pictures, contacts etc. to a server somewhere. Sure, maybe that was mentioned in the long EULAs, but it's not practical to read through all the EULAs everytime I crete an account.

In addition, the 'Samsung account sync' app was installed on default, so I didn't even get to accept the app (or even read what access rights it had).