What exactly does the max towing number mean?

I have the 2.7 with 3500lb max towing.

How exactly is that number determined?

Is that the safest weight where a brake controller wouldn't be needed?

Or does that number mean max, as in use extreme caution when towing this amount?

Just looking for explanation of what that number really means in real life application.

 

Somebody else can chime in and explain more in depth but that's the maximum Total weight Toyota has calculated including trailer, that the Vehicle can tow with, without doing harm to the vehicle, i.e. The engine, transmission suspension and frame.