Not all the time. But when I'm towing, 100% of that time. It makes a meaningful difference for high load situations. Makes it easier to drive, as the throttle tip in is way more aggressive, and shift logic changes in that it holds shifts to higher rpms. I'd bet it also keep VVTi primed towards the power end of timings too.
To Markuson's point, mounting big tires also presents itself as higher loads to the driveline, and ECT/Power will help there too.
I remember in my LX470, which doesn't have as much power, it notably helped even for 33's. On my LX570 with 33's, it's a bit aggressive making modulating the throttle for smooth inputs still a bit edgy. There's been several occasions coming back from a towing trip, where I forget to turn it off after unhitching, and the wife is confused why it's so jumpy.
No problem in doing this. There is a hit to gas mileage though.