iCloud, a popular cloud storage and computing service from Apple, acts as a syncing center for all your contacts, Emails, calendar, reminders, notes and application data (Pages, Numbers, Keynote etc.) present in your iOS Device viz. iPhone, iPad or iPod Touch.
A free iCloud account has a storage limit of 5 GB and by default, iCloud automatically synchronizes all your device’s data to its cloud servers, which often results in syncing of data that you do not want to backup! As a result, your backup size increases and your online storage space decreases!