This plug-in simply introduces visual clutter, and distracts from being able to focus on content. It is retrogressive and backwards-facing (both at the same time).
on the other hand, it makes it easier for your site team to do their work quickly, it makes the forum functionality more accessible to people who are vulnerable or under-confident when using a forum platform. It helps to prevent the software getting in the way of the message. And of course, dare I say it, it gives you a choice either to use it or not.
Edit: if you want to restore post numbers to your new upgraded version 4.5 then go here---