If an app is opened but it loads data which is not asked for, and uses my precious data plan to store the background data into cache of phone, it wastes data charges for stuff which user does not require?

Do apps do this or only foreground data is loaded into cache? For e.g., if Feedly is opened, it does not load even background feed articles into cache by using data charges. I understand that each app have settings to prohibit app from loading data in background (data not required or asked by user). But on finding Feedly, such options were not noticed.