When your iPhone or iPad warns you iCloud is running low on storage space, you can avoid buying more space by changing what iCloud backs up.
Over at the How-To Geek, they suggest looking at the app data iOS backs up. Some of the apps are already cloud based and don't need backups from your device.
To see how much space your apps are using, go to Settings > iCloud > Storage & Backup > Manage Storage. Tap your device under Backups. Then, under Backup Options, tap Show All Apps. You'll see how much data each app is using on iCloud.
I tested this out and found that Evernote took up 1.2GB of iCloud backup space. Since Evernote is already cloud based, I don't need it backed up by iCloud. If I need to restore my iPad, I can download that data again from Evernote.
Even if you aren't running out of space on iCloud, you might turn off some of the cloud based backups. A streamlined backup saves time and bandwidth if you are on a metered or slow connection.
How to Free Up iCloud Storage Space [How-To Geek]