Those free apps on your smartphone can be really great, especially when they're used every day because they're so useful. But if you are on a limited data plan or you're running out of battery power on a daily basis, those free-ad driven apps could be a bad idea. They can cost you dearly by eating up your battery power and limited data plan. A report by researchers at USC and several other schools revealed that those ads in many free apps use up to 79% more of your precious data plan than apps that don't have regular ads in them. The report went on to state that they can drain 16% more of your power and use up to 22% more of your phone's memory in order to routinely deliver new ads . If your smartphone is sluggish and always seems to be running out of batter power, those free games could be a big reason why. There's also a privacy component as well, because free apps often request more permissions generally for advertising purposes. So the next time you're choosing an app to download, ask the question: To pay or not to pay...