I have a iOS app where I need public_content permission to search users and tags. My application allows user to create posts and add popular tags and users to caption. here is screencast https://www.dropbox.com/s/k330dye9sbn6mz1/API%20use%20Mosaico%20public%20content.rtf?dl=0
API Usage
First API : media/popular = we are using this to get popular media. Based on that we are preparing a list of tags for "trending" (most used), to be used as auto suggestions in the caption edit mode.
Second API users/search = we are using this to create a list of auto suggest @ mentions in caption edit mode.
Third API : tags/search = we are using this to prepare a list (in alphabetical order), to auto suggest to the user based on a tag the they entered in caption edit mode.
And reason Instagram gave is
public_content: This permission (public_content) is only granted to apps that enable brands, advertisers, broadcasters and publishers to discover public content. We do not grant access to apps that do not fall into these categories. Please review our documentation (https://www.instagram.com/developer/review) for more information.