Syncing/back-up is like insurances, doesn't really matter and seems like a waste... until something happens. Some and probably many people today live through their phone, and if its damage or lost and you to enter contacts into a new phone or need a number you can't remember... OUCH. You can turn off Auto syncing and do it manually if you want, i know i use my Verizon website to send messages, check my account, usages, pay my bill, so my contacts being available on line is great.
If you have no need for it... turn it off. I turned off my weather Auto-syncing... if i wanna know the weather i speak into the mic and get it off the internet or from the news (tv).
When someone NEW or a new phone number calls me, my phone ask me if i want to add it to my contacts, this comes in handy on a moments notice.