There was a moment when a lot of off-topic was posted in a topic, and there were semi-off topic/on-topic replies in it.
I then created the:
In reply to now deleted post(s):
This is an example text in the [replydeleted] tag
I edited the posts that reactions were based upon posts that were now deleted and made it so that it still looks ok.
So basically I use it in situations that I want to delete posts, but where I want to keep some of the replies.