> As an iOS developer who worked with apps that access camera frequently, I can confidently say that it's just a UX optimization.
Here's what Facebook does once you give access to the iOS Photos app. Every time you open the Facebook app, it asks you - "Would you like to post these photos on Facebook?". Basically, they are reading the Photos library repeatedly to scan for recent (or past) photos along with their meta data. It could be just UX optimisation. It could also be UX optimisation for harvesting data.
Here's what Facebook does once you give access to the iOS Photos app. Every time you open the Facebook app, it asks you - "Would you like to post these photos on Facebook?". Basically, they are reading the Photos library repeatedly to scan for recent (or past) photos along with their meta data. It could be just UX optimisation. It could also be UX optimisation for harvesting data.