Keeping this all in my head - even remembering how many shells I had open to do what - takes more thinking and effort than I want it to. It is far easier for me to just say, "This is where all the stuff for X goes" and physically isolate it from everything for Y and Z. And when I go back to it, it's all where I left it. I find this a much easier workflow.
I found it useful, especially with Clojure and vim. The splits are nice everywhere, and it's way better to be in the habit of opening a tmux/screen when sshing.
That workflow is also why I hate OSX updates that force a reboot, which piles all the terminal and Chrome windows in one desktop. And then it's just an update for RAW camera files or something that I don't care about, but it nags me every day. /rant