Sync contacts in Exchange account?

Hello,
I have added my bank's Exchange Account in Email App,
While adding the account I unchecked Sync Contacts,
What will happen of I check (enable) Sync Contacts?

- only contacts saved in my exchange account will (Sync) to my device??
OR
- my mobile contacts will also Sync to my Exchange Account?

Using Moto G with Lollipop 5.1.1.

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