As a sysadmin I am offended when media attachments don't load, but as a user I'm delighted when the posts still make sense thanks to image descriptions! :D
This is yet another reason to write media descriptions whenever you can--large files can get lost in transfer and bandwidth/capacity varies widely between instances, so your media are not 100% guaranteed to federate. Your descriptions will make it through much more reliably, however, keeping your post useful even if the attachment is dropped.
A small instance for writers.