cellular data settings

No. It can be on whichever setting you need it to be.

If you set it to Data Only, then its only used for Internet Access. If you set it to Voice & Data, then it will be used for both if you carrier supports it.

If you turn if off, then you won't have internet access when away from Wifi.

As I said, Data Only, means it will only be used for Internet Access. It refers to the 4G / LTE connection.

If you set it to Voice & Data, then it will be used for both things. Voice Calls and Internet Access if your carrier supports it.