Request Private Access - this button allows users to send a request to share private images with the profile owner. If the owner accepts the request then both the sender and the receiver private images will automatically be temporarily opened to each other for 5 minutes.
This feature is design to reduce the games users usually play with private images where someone promises they will open their private images if you open yours first but after you open yours they do not open theirs. Now you can use this feature to make sure that you only grant access to those who give you access.