That way, you can yank/put easily using the usual shortcuts from any tmux window to any tmux window. Then, it's usually easiest to only use intra-process pane splitting (keeping it all in vim or emacs) unless you need to do something that doesn't follow a perfect division, like:
top half vim / bottom left vim / bottom right trailing logfile
or something.
More than happy to write a blog post, if you're interested.