I find tmux makes less sense within a tiling window manager because then you have two contexts effectively providing the same functions (or three, if you use vim :split (or four, if you use tilix)).
I also use a tiling wm, and use tmux. The main reason is that it means I can easily transition to using the same tool when working with remote machines using mosh. Personally, I've always felt odd when trying to use i3 tiling for terminals (maybe that's because I used tmux before I used i3).
