When you have Wi-Fi and cellular data on at the same time, does it use cellular data?

If I keep my cellular data on and also have my iPhone connected to Wi-Fi, will it use any of my cellular data?

It only uses Wi-Fi, but you should turn cellular data off anyway because when ever the phone is sleeping it will switch to 3g to save battery, and that can use a lot of data if you don't have unlimited.

Should data saver be turned on or off