Grinding is better for the environment than other methods of stump removal. Some people use harsh chemicals to kill the roots; others set them on fire. Needless to say, both of those methods are ecologically irresponsible, not to mention dangerous for the one performing the removal.
When you grind a stump after your large tree removal, you will discover that it takes less time than other methods. This is because grinding the stump down makes it easier for the roots to decay and break apart naturally. That is why it can cost less.