iOS data usage specifics - iTunes Accounts

I'm trying to find out what does "iTunes Accounts" traffic stands for on iOS, since it has gobbled 850MB on cellular data in 13 days. I have iTunes Match on but have disabled the Music app to access data on cellular networks. I'm on iOS 8.3 since today, data was consumed on 8.2.

Probably iTunes & App Store background downloads.

You can prevent these, so it only updates when you're connected to wifi, in
Settings > iTunes & App Store… by disabling Cellular Data
[I also prevent all automatic downloads, so mine only updates from iTunes itself, on my Mac]

Seems like it might be iCloud documents syncing Settings -> iCloud -> iCloud Drive (scroll to the bottom to turn off cellular data).

Also seems like iTunes music "new music mix" might come in under this.