Supply to an outbuilding, It's in a duct "buried" in gravel between a patio and a fence, so no chance of accidentally JCBing it, so it doesn't need to be armoured, and it will be easier to pull through the ducting than SWA.
Inside the house it needs to be singles as they will run in surface trunking behind kitchen units, including a 90° bend. I could join to singles at the point of entry, or I could just carry on with the cores of the cable, unbroken.