I'll answer DS.
We don't click on that button to do it, which is why I didn't know about it .... as BM says it is not is clicky button but an indicator that will show up on the thread that has been redirected. Same as the two in front of it .... they are merely symbols to guide users. That row is a "Key" to symbols by way of explanation of what you might see next to posts.
Who can do it? It is something that only Admin can do .... if, for example, we combine threads.
Why might a board be "redirected"? If we feel it necessary
As to how ..... by waving our magic Admin Wands and to where? ~ Anywhere we feel is more appropriate
In Wenchy's day much would have depended on hormones I 'spect so the answer could have been "anywhere we damned well feel like.
"
I hope that covers it all.