But yeah, that's pretty much my objection -- it's not a big one, and there's room in the world for more than one type of software. I'm aware of tmux, but it just shifts the problem from vim to tmux: once you need to upgrade tmux, or your OS, or your computer, everything you've set up gets lost, and I really don't want that to happen.
I'm also aware of things like teamocil, and I even used itermocil for a while. But it turns out that the kind of environment edits I like to make are ones that I just do, rather than ones I can specify in a config file then restart to set everything up again. For example, when you say:
> If you are just exploring the code base or making small edits here and there you don't really need persistent tmux session for that.
Coincidentally I do have a relevant example for that. Last week, when I was exploring the files that make up the zoneinfo database, I put the files that I needed to keep referring to (of which there were like 5) to the side, knowing full well that they wouldn't go away. Then they just stayed there for a while as I got distracted with other stuff. This week, when I had to return to it, they're still there; and all the files from the other projects I'm working on are all in their positions, too, ready for when I switch back next week, surviving through a system restart and an editor upgrade.