If you press the "Start" button many times it may lead to malfunctioning of the software. In order to prevent this from happening and even in the case of you accidentally pressing the "Start" button many times the software will show a error pop-up message as below.                

Example

As you can see the software is already working and even if i try to press the "start" button again, it will not restart and show the error pop-up! This way the software will not perform a bad operation and work smoothly to complete the current operation before you can start again either by stopping the software & restarting it or restarting a new operation once the software by itself finishes the current operation.