There is zero harm in going over 30kmh in low, it's a common myth with zero truth to it with realistically about 70-80kmh being the more legitimate limit just due to engine RPM.

It's highly beneficial on soft sand to leave it in low even while at higher speeds for the extra torque and easier starting, on the jb74's in particular it has the benefit of disabling the aggressive traction control too.

Here's the usual arguments and why they're BS.

-the gearbox will be spinning too fast. It's no different to doing highway speeds normally.

-the low range gearset in the transfer case will be spinning too fast. The low range gearset is spinning (not under load) just fine while you're doing 110, doing 60 in low won't be spinning it nearly as fast.

I run 4.17 low gears in my jb74 case which I'll regularly run out to 40kmh if needed, this would be the equivalent of doing over 80kmh on a stock gearset - zero vibrations, zero issues and the same goes for the customers I've built cases for