iOS App Install confirmation is a feedback mechanism which enables customers to receive confirmation from Google every time an iOS app install event can be attributed to an AdWords ad click or view. Why would an advertiser use this solution?

Q) iOS App Install confirmation is a feedback mechanism which enables customers to receive confirmation from Google every time an iOS app install event can be attributed to an AdWords ad click or view. Why would an advertiser use this solution?
Ans:

The advertiser is interested in cross-device conversions.
This is the only availabe method of conversion tracking for iOS.
The advertiser wants to count calls as conversions.
The advertiser is using an in-house or third party app analytics system.