Garmin Fenix 3 Heart Rate (HR) Silver

Is it possible to use the watch as only a timepiece? So if its "turned off" (no GPS or notifications, etc...) it'll only display the time?

If the f3 has built in hr, why buy the hr strap?

Does the wrist hrm work for swimming or do you have to use the chest hrm?

Does it work with polar bluetooth hrm or does it have to be the one for garmin