Expedition Overland recently blogged about an eye-opening incident in which proper use of their recovery winch became an issue. WARN even shared this story on their Facebook page because this is such an important lesson.
After the trailer nearly pushed their Land Cruiser off the side of the trail due to slippery circumstances, another 4wheeler offered to help right the vehicle by hooking the Land Cruiser's winch line to his truck's bumper and pulling.
A recovery winch is plenty strong to extract a vehicle, but it is not intended to be used as a tow device. The shock-load forces that travel through tow straps to the recovery points on your vehicle are many times greater than the steady-state forces that a winch exerts during a proper recovery. The winch drum's brake is not designed to absorb forces beyond the winch's rating and could result in damage to your expensive winch.
WARN's own advice:
WARN: When you introduce a quick, sudden load to a winch, that's called a "shock load." Imagine taking a piece of rope in both hands, then quickly pulling it taught-that's a shock load. Shock loading is very stressful on a winch's internals. Proper winching gradually places a load on the winch, which is how it is designed to be used. You should never use a winch rope for towing due to shock loading. While you may have the best intentions of gradually introducing the load while attempting to tow a vehicle, the vast majority of the time it doesn't happen that way, and the winch will receive shock loads. Always use a proper tow strap for towing. For those attempting a recovery with a strap, be sure to have the proper unit as well. Recovery straps will have a bit of elasticity to them that allow for that rubber-band effect that aids in recovery. Tow straps do not have that elasticity.
I have a WARN M8000-S winch on my own Jeep's WARN Stubby Rockcrawler Bumper. The winch itself is rated for an 8,000lb. line pull, and the synthetic WARN Spydura synthetic winch line is designed for a 10,000lb. winch, but I use an inexpensive Smittybilt recovery strap rated for 30,000lb. pulls when I'm towing vehicle-to-vehicle. The WARN front bumper has two ultra-strong recovery points to attach D-ring clevis shackles included in the WARN recovery kit.