Security! When you think apps ask for loads of permissions and then make their privacy documents so long winded and hard to read that we give up. Then we have Google or other providers backing up all our data. I always try to limit what they back up but press one wrong button and you've handed them your life and a lot of your contacts info on a plate. I've just had a new phone and I've realised how much of my life is on the old one, such as the calendar and my contact list.