Yeah its a nice feature to have when you have a small community because you only ever see a few users in the browsing user list.
However once you have a forum where a topic has >500 users it becomes useless and just a unnecessary strain on server resources like julian said.
We will probably bring it back as a plugin.
i see, thank you for the info
if you planning to remove functionality in favor of big communities maybe this could work too https://community.nodebb.org/topic/6920/about-topic-follow-notification-spam/