this has always bothered me, but i suppose apple don't want users to have too much control and then wonder why things aren't working. but i would really appreciate these categories as things you can switch on/off (a bit like the privacy options, but i suppose these don't really pertain to privacy).
now that FB messenger and whatsapp offer VoIP, i suppose they must also take advantage of the background VoIP privilege. now i don't know how much battery this really uses when idle, but it must use some (plus they could exploit it for other tasks) so i'd be much happier if i could deny them this privilege in Settings as i don't need that feature of the apps, only the text messaging.