Nature, close up portraits vs anything else on the kit lens...
Do you think it's worth keeping? I don't think my wife or I would be the type to swap lenses in and out often. What type of pictures would come out significantly better with the telephoto lens vs. the regular 18-55 mm lens?
+1
I'd say perhaps play around with it a bit and see. Do you have children?
Take your kid outside and use both lenses and see what you like.
Even if you don't end up using it that often it's still a good deal for $50.
On the other hand if you're never going to use it then obviously you're missing out by not selling it.