I suppose that if he used it continually operating under a continuous load it wouldn’t much matter because it wouldn’t last very long but if it could operate non-continuously it would continue to last for a while.
To be able to do what he is questioning would take a math wizard and the unit would be drawing current continuously.
Through this statement he shows the understanding that should the heat be sized to low that the heat would never shut off.
Does this answer your question?
The bigger the temperature difference, the bigger the heater required to maintain a temperature if left on continuously. Since most of these things aren't variable, that means turning on and off. Then, throw in wind and air infiltration, and it becomes more variable. As has been said, the things tend to burn out when run continuously, so sizing them so that they can turn on and off as required, is the prudent thing.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013