What and When
You can only be relaying a Mayday if another station has transmitted one.
If you spot a liferaft or small boat in the water you cannot be sure if the craft requires IMMEDIATE assistance or not. Clearly, should you be concerned then the matter needs investigating urgently. An URGENCY requires a PAN! Take a scenario where you ASSUME a distress and helicopters and boats are launched to rescue. It turns out not to be the case for the Dinghy was being used for fishing. Meanwhile another genuine distress is transmitted. The Helicopter is not now able to attend immediately until it has refueled and the rescue boat is now going in the opposite direction. We now have a mess. Make the appropiate call and allow the professionals to deal with what THEY are trained to do. They do it bloody well!
As i have already explained the RT test encompasses much more than the student will normally have experienced during training. Such as the correct use of the wider system where it is sometimes found not to be understood.