As a developer that often browses the forum for work, it’s tiring to see 3 of the same posts in the #collaboration:recruitment category back to back.
Many of those are spammed because newer users are unaware of this option, thinking that there’s something wrong with their posts. This results in spamming the same post 3-5 times until the user either catches onto the fact that this is automatic or asks in #forum-feedback:forum-help.
One of the ways this can be done is by editing the template to include a note about this. Another thing that can be done is to change the text displayed with the automatic lock to make it more obvious that all posts are locked. Alternatively, Discourse allows admins to toggle reply permissions for trust levels and toggling replies to off for everyone. While this would make the user unaware at first of the fact that one can’t reply to the post, it would certainly be less invasive and too a degree prevent spamming because “my post was locked”.