This sums it up nicely:
Prior to iOS 5, sharing an Apple ID wasn’t really a problem because its main purpose was for purchasing content on iTunes, using it for support purposes and purchasing items on the online Apple Store – all tasks that worked fine when sharing an ID.
[Source, macstories, iOS 5 & iCloud Tips: Sharing an Apple ID With Your Family]
That sums up our approach pretty much to date. But here is the problem:
Now that Apple ID is tied to a bunch of services, a lot of which involve personal and private data that you don’t necessarily want to share with others – even family members.
[Source, macstories, iOS 5 & iCloud Tips: Sharing an Apple ID With Your Family]
And because paranoid society is paranoid, children under 13 cannot have an Apple ID.
Additionally:
The other issue is that iCloud involves a lot of data synchronization and this doesn’t work well with multiple people as it results in data conflicts and devices syncing data (such as calendar events) that are meant for another person in the family.
*emphasis added [Source, macstories, iOS 5 & iCloud Tips: Sharing an Apple ID With Your Family]
Naturally, each owner of an iDevice wants to be able to use services specific to that user. As parents, we want to control when the children purchase, how much they spend, and we want to simplify the syncing of their devices without having to put a Mac in each room of the house. There are six services that use an Apple ID:
- iCloud
- FaceTime
- iMessage
- iTunes Home Sharing
- iTunes (includes App Store and iBookstore)
- Game Center
Read section 3 from this great article
