As your forum get bigger your post table get big and in to unmanageable sizes which gives lot of performance issues and corruption risk with high server load. So its great if we can have a archive option for old threads/any thread admin like. Xenforo can move those threads to separate archive table of the mysql database. Those threads are read only. If you want to edit or make any changes then you have to get them back out of archive. I have seen this in some other popular forum software and i have noticed large performance gains and low server resource usage due to this. Really like to see that feature in Xenforo too.