It depends on your logic, I can say.
Consider that you assigned the I0.0 to your "Start" Push Button. If you assign I0.0 somewhere else in your logic to "Stop" Push button, after you download your program to the PLC and push the Start button, then your equipment will Start and right after that will be Stoped. Because you have assigned the same address to two different Push Buttons with two completely different functions.
So, in this case, you have to assign I0.0 to your Start Push Button and another address such as I0.1 to the Stop Push Button.
Overall, if you assigned I0.0 to your Start Push Button, then anywhere in your logic, if you want to point out to Start Push Button you have to write I0.0 and no other address.
Hope I have explained clearly enough.