I have Facebook Messenger installed on my iPhone. Going into the storage settings of the phone reveals that the app is currently taking up over 2GB, making it the single largest app on my already strapped-for-space phone, which is pretty steep for a messaging app. Delving deeper reveals that the app itself is only 127MB, and the rest is taken up by Documents & Data, which in iPhone terminology is the data that a given app works with; here it can only mean the actual conversations stored, including any photos and videos.
So, I'm wondering whether it's possible to delete messages from the Messenger app in order to free up some of the space being taken by those conversations, without also having those conversations be removed in the web app? In other words, does deleting messages from Messenger also delete them from the web app?
Best Answer
TL:DR; yes, deleting messages in Facebook's Messenger app also deletes them from the web app. Presumably, this also means it deletes them universally across a Facebook account, no matter what tools or applications you use to access it.
For what it's worth, it also does it pretty damn fast. To test, I went ahead and deleted 5 conversations from within the Messenger app on my iPhone 5, making sure to also have each one open in my desktop browser as I did. No less than a second after deleting the conversation in Messenger, the desktop browser refreshed in real time and the conversation was removed from there, too.
The unfortunate implication that this has on the size of the Messenger app is that the more messages you allow to build up in your Facebook account, the proportionally larger the size of the Messenger app on your phone gets. This could have unwanted ramifications for someone who suffers from the unfortunate combination of messaging as much as I do and having a phone with limited space. As mentioned in the question, my Messenger app is currently over 2GB.
The solution, if you really need to free up some of that valuable space on your phone, is to actually delete some of those messages (not to be confused with archiving, which still keeps messages stored), although obviously sometimes this just isn't feasible. Imo, this is pretty bad UX on the part of Facebook, but it is what it is.