To help other road users know what you intend to do
If you wish to turn right into a side road take up your position in good time. Move to the centre of the road when it’s safe to do so. This will allow vehicles to pass you on the left. Early planning will show other traffic what you intend to do.
B To allow other drivers to pull out in front of you
C To give a better view into the road that you’re joining
D To allow drivers to pass you on the right