For me there concept of fixed sampling time is crucial for the use of control system engineering in controlling some particular plant. This is done is a fixed sampling time for a discrete digital control based in a microprocessor. If the sampling time is varied, it will affect the gain and such.
Probably this is my thinking and this is the paradigm I am stuck in. But there actually exist another type of method called the event based control. This control method does not need a fixed sampling time to control a plant.
I am still studying on this matter because it is seems complex... ><
Credit to Kian Sheng, my senior for introducing me to the concept of event-based control.