Account Sync Question

[Sedp23]

Still relatively new to Android, what exactly does leaving account sync on do for each of the apps there I'm noticing Skype, Cortana, email, facebook, twitter , imo and a few others are there

What exactly are facebook twitter and Cortana syncing? Why do I need these apps to sync? What do I lose by cutting them off?

I know onedrive is on and probably syncing photos backing up pictures I take but what about other apps

 

[rhapdog]

Cortana uses the sync feature to keep up with who your contacts are and scans your emails to find appointments and such. If she doesn't have your contacts synced, then you can't tell her to "Send an email to John," etc.

Skype, likewise, needs contacts synced so that you can contact people using Skype. Email, same thing. Facebook and twitter want to sync with contacts in order to "help you locate your friends" on their platforms. I always disable that permission for social apps, as I don't need help finding friends. I know how to find them, and I don't always want others finding me.