Apple - Why is so much "Other" space occupied on an iPhone 4?

Factory Reset

I ended up doing a Factory Reset to clear off the "Other" data.

The key is that since the Other seemed to be backup related, I did not restore the phone from the backup. Instead, I selected "As a new phone".

One by one, I added back her apps, music and photos, watching the Other bar like a hawk.

The Other data remains virtually gone now only taking up 430Mb.