Ground taxi requires wheels. If you have them, ground taxi requires less gas. Your local helis ground taxi because they can and it is cheaper
No, not necessarily true. Very often, wheeled helicopters ground taxy
only because ATC local procedures require it, for example I am usually required by ATC to ground taxy to the runway in use for departure and landing when I have no other need. This often means wasted time and fuel, and unecessary wear on the tyres and brake components.