TLDR: While Fediverse won't directly serve you ads, anonymous bad actors other than Meta can save, redistribute, and even dox you for any information you post here. Anything you post here can/will remain forever on some malicious instance that doesn't honor deletion requests.
So be careful!
The post title should really be "The Internet is a Privacy Nightmare If You Think You Might One Day Want To Send a Takedown Request to a Malicious Site".
YSK that deletions are federated just like everything else. If you delete a post on your home instance, that deletion request is sent to all other instances that federated properly/are not malicious, and your post will be deleted from those instances as well.
YSK that images are only ever stored on your home instance. All other instances only link to the image on your home instance. So deleting an image deletes it from the server and breaks the link everywhere.
Wait..the posts i send are "stored" on other instances? Inthought they were stored on just one and just accessed by the others? There shouldbe no need to delete from other instances. Once the post is deleted from ist home instance it wont show up on others anymore (because it was never stored there). Am i misunderstanding this? Like most, im new to Lemmy amd still figuring things out.
Each remote instance stores the posts from every other instance's communities, from the point at which the first person viewed (...or subscribed to...?) that community on the remote instance. That way the instances are less dependent on each other's uptime and can optimize their queries, giving a better user experience.
Btw. this also means that there will always be some delay before posts/comments from one instance show up on another.