If you grant an app (any app) complete access to your photo library, you are essentially giving them permission to do what they like with your photos, within the terms of their privacy policy - because they all stick to that
An app such as Facebook, for instance, could access the geographic location of your photos, upload them to their “private” user storage location and so on.
The reason Apple and Google are giving users more control and in some cases, enforcing that apps explicitly request access with a proper description as to why. Is to try and limit the amount of information these companies can scrape from you - it’s all money to them.
Unless you’re using something like Google/Microsoft/whoever for a backup of your library. I’m all for making one library, adding photos you want to share into it, and only allowing them access to that library.
It’s scary just how much information can be collected and how much they can track you, if you don’t pay attention to the prompts and more importantly, their EULA and privacy policies, instead just hitting the, yeah, yeah, just let me use the app button.
Go read some of them when you have spare time. They might be (are) boring, but they’re an eye opener. It’s why I don’t use Facebook (among others).
Don’t get me wrong, I have no problem sharing information that’s randomised and not linked to me in any way, for the purposes of app/service improvements. But though I have nothing to hide and very little of interest to others, I’ll be damned if I let them do the digital equivalent of burgling my house…..
….. But that’s just me. I’m clearly in the minority there.