The growling is a good tool for expressing a lot of different feelings that may be hard to express with normal vocals. For example, Opeth, use growling and clean vocals to express different moods. Listen to any song of "My Arms Your Hearse" to get the idea.
Getting used to growls isn't that difficult. I myself didn't like them at all before I started listening to Opeth, and now I think growls are a great tool.
Here's Opeth's "When.
http://www.youtube.com/watch?v=2G2jlXUkJ84&search=opeth
Now I lay me down to sleep
Blah, blah, blah my soul to keep
If I die before I wake
I'll go to hell for heaven's sake