One of the main advantages to use CPI campaigns for new apps is the possibility to get the keywords into the index. As you may know, usually new apps on Google Play are not indexed for the keywords at once after publishing. You can set CPI campaign for your new app in low CPI countries which may help to get into the index not only in the geos you get installs from, but in other regions as well.
CPI campaigns will be also helpful if you need to increase the number of downloads on the app listing page (for example, to get 5000+ instead of 1000+).
