No harm whatsoever in using 2low. There's no 'balance' needed. The internals of the case make it a direct-drive through the t-case to the rear output shaft. Engaging the low range planetaries just adds a gear reduction, but the power flow is still straight through the case.
The transfer case clutch coil couples the front ouput to the rear output to get the power to the front wheels. (and if everything is rolling, there's little to no strain put on the case until the rears lose traction.)
Practical uses:
-Disconnect the front driveline for tight maneuvering in 4low. On a tight trail, it's a lot less hassle than shifting out of 4low, then back in when the going gets rough again. Simply flip the switch (on the fly), make the corner, then flip the switch back on (again, on the fly).
-Backing a trailer into a tight space, or maneuvering the Ex up a hill (or through soft ground) while trying to hitch up.
-Maneuvering on soft and/or slippery grass without tearing it up with the 4wd locked.
-Any other time when you need the gear reduction of low range, but not the driveline bind-up that comes from maneuvering in tight quarters.
It does not save gas. If you have uneven-sized tires on it, you're doing something wrong to start with.
