u mean at any time only 1 sensor is only allow to work?
No. All the sensors work, all the time, regardless of whether the Arduino is paying attention to them, or not.
But, suppose you had a clock chip. It's happily keeping track of the time. You have an LCD, too. It's displaying the time. You have a couple of buttons. You want to make a stopwatch. You set one button as the start button, and another as a stop button.
When the start button is pushed, the Arduino should start displaying the elapsed time on the LCD, instead of the current time, and should start looking for the stop button to be pressed.
Now, it's important to get that stop button press when it happens, not 10 minutes later.
So, you might be tempted to implement a while loop, to wait for that button press event. That becomes a blocking activity though, in that nothing else can happen until the button is pressed. The LCD can't be updated. No other sensor changes matter. Generally, that is not a good thing.
This situation is why interrupts were developed.