The block's edit component fetches data that is needed both on the front end and back end. The block already includes tag ids, but in WYSIWYG version a new "tags" attribute was added, in which the complete response of the tag query the editor does is stored.

Because the block is still back end rendered (which is a good thing) it has a fallback where it fetches the needed data for older posts. This means we don't need to store any additional data at all except for the already existing tag IDs.

Even if there is minimal data on a tag, it's still a lot of additional completely unused data being stored. If an instance has a lot of data on a tag (e.g. large description, much meta data/links) this can cause more severe issues.