Because : It does exactly what it says.
So if it's 3am and you forgot you have a 1/2 dozen timestamps formatted as HH:mm and a dozen dates formatted as dd/MM .. all for very good reasons... then be prepared to spend an hour going through your 50+ BO's to make sure you changed them all back so they fit into the columns on your queries.
Bonus Tip : 'Take from Locale' doesn't work in a Calender Widget on a VP
