What is catch and throw used for in Ruby?

In most other languages, the catch and throw statements do what the begin, rescue, and raise statements do in Ruby. I know the you can do this with these two statements:

catch :done do
  puts "I'm done."
end

and

if some_condition
  throw :done
end

But what is this useful for? Can somebody please give me an example of what catch and throw statements are used for in Ruby?