Syncing Photos causes "Other" to explode
This actually started with iOS 8:
When I have photos syncing to my iOS devices, the "Other" category explodes. Without photos synced, my "Other" space usage as shown by iTunes typically hovers around 750MB. With photos synced, it explodes up to over 5GB!
I am currently syncing about 5400 photos (basically, almost my entire digital photo library). The usage bar in iTunes says that's 909.6MB (of resized) of photos on my iPhone 6 and "Other" has 5.1GB. When I remove the photos, "Other" shrinks to less than 1GB. It's annoying on my iPhone 6, which is a 64GB model, but my iPad 2 is only 16GB so that extra wasted space is a real usage issue.