All AWD systems will help with additional traction, but the layouts have dramatic effects on handling. Most AWD systems induce understeer, but some can actually help a car handle even better.
Marketing departments often fib about the capabilities of their company’s AWD system. In most cases, no, your car can’t send all of its power to just one axle — unless the other axle is in the air. Manufacturers often leave that little detail out.
To understand what your car’s AWD system can and can’t do, you need to understand its base layout – if it’s a FWD-based car, like a VW Golf R, that happens to have AWD, it can never decouple its front wheels — only add power to the back. It can send 100% of its power to the front wheels, but never more than half to the rears.
If it’s a RWD car like a BMW 3-Series, it can never decouple the rear wheels, only send some power to the fronts. It can send 100% to the rear, just not to the front.
Then, there are fixed-AWD systems like Subaru’s “Symmetrical” AWD. That system sends power to all four wheels — but can only send it all to one axle if the other is, you guessed it, in the air.