ok so I did a small test, I drove a month with it on and a month with it off, for those who worry about consumption it made no difference
I prefer it on as it holds the gears longer on up change, and changes down earlier, I prefer this as sometimes it feels like the car is in too low a gear, which is I assume what Lexus want for their quietness and comfort levels
I find it handy on the motorway as the car is ready to accelerate quicker and if you (occasionally) floor it, it knocks it down a couple of gears
I also find when you are braking coming up to roundabout for example it changes down quicker
The switch really is a 'however you feel you prefer to drive' switch
SWMBO tuts when shes see its on, so its worth having on lol
BTW I'm 51 and not a speed freak, It just suits me