Sway has nicer configuration for multihead display setups than you ever get with xrandr, which is very nice on laptops if you often connect to different external monitors. There's also some clunky support for moving windows around with the mouse, which I've found to be occasionally useful.

Then there are the wayland advantages: very little screen tearing if any, no blanking the screen when connecting to a new display, better security properties.

There's disadvantages as well. There's no xdotool support, and if you want to use any sophisticated keybindings or remapping keys, you'll be forced to rely on Sway's configuration language to do that for you. On i3 I was able to bind ctrl_r to right click, but that is — as far as I know — not possible on sway without rewriting the libinput event stream, which is very painful.