I have started to check my calorie intake, is this bad?

i am 16. And i found this very useful and cool app for the iPhone called The Calorie Tracker and now i am going to be tracking every calorie i have or am about to have. Is this bad? is it a good thing? because i was thinking then wont i always check my calories and then sometimes say no to a lot of foods ? btw i am trying to lose weight, well i have but i am still going to. i weigh 79KG male. Thanks !