All-wheel-drive and four-wheel-drive vehicles have center differentials that require all four wheels to rotate at the same speed. Wheel-lift towing lifts two wheels off the ground and drags the other two — the speed differential destroys the transfer case.
Repairs run $3,000–$8,000 depending on vehicle. Some manufacturers (Audi, Subaru) explicitly void warranty coverage on transfer cases that show tow damage.
If you're not sure whether your car is AWD, tell dispatch the year/make/model. We default to flatbed when in doubt. Same $249 / hour rate either way, $224 first hour online.