I clear you to land , the runway is clear.
But I'm going too fast to stop in the available distance/ there is a sudden gust/crosswind which I am unable to cope with, so it would be unsafe for me to continue without hazarding the aircraft or pax. My call.
I send you around ,the runway is occupied which would prevent a safe landing.
If by going around I would be putting the aircraft into flight conditions which I cannot accept or which the aircraft is not cleared for - and my judgement is that I can land safely without hazarding the aircraft in front. It is still my call as I am responsible for the safety of my flight.
You as an ATCO are responsible for providing separation - I am responsible for the safety of the aircraft, its passengers, third parties and for collision avoidance.
