Thank you for quick response!
for 1 & 2, I'll try to explain it a bit more specifically.
for 1, I was basically thinking of private variables that is not related to any objects in any way or form, but their numbers do exist (though invisible), so I can use these sets of variables to use them as a sort of a 'trigger' mechanism, so I can tell A.I to behave in specific way when it is triggered. Taking for instance, an RPG game where you have specific characters in your party, and for each character you have it turns the trigger on (and off for characters you don't have), and the event sheet will check if those triggers are on, and will play certain events for you accordingly (that is related to the character).
I guess it can be done using global variable, but without any way to organize the variables in directories, it could get cluttered i think.
and as for 2, i was thinking in the line of - a strategy game for instance, where many warlords have their own set of private value called 'gold', and each castle also have their own 'gold' private value. so instead of having multiple private values of same concept (and complex event sheet programming that follows for 'transferring' that variable) , i thought it would be handy to have a global variable which each objects can gain or subtract individually, and also works globally when needed. I know it sound a bit fuzzy but I hope i explained it well