I find myself using the Vector3 variables inside an FSM to setup "way points" for various things, eg. next place for a camera to animate to, next Euler rotation for said camera, etc.
Rather than trying to copy out the individual values from objects as I place them around the scene, or drop a whole bunch of empty GameObjects in the scene to use as markers, it would be really handy to be able to just have a toggle on the Vector3 variable rollout (like the Inspector Toggle) that placed a movement handle into the scene. That would allow us to position these Vector3 variables with a lot less hassle. Possibly also the ability to toggle it to a rotation handle as well would be handy.