[Bear_in_RoseBear]

Ungoliant (confirming my suspicion that she was only introduced out of thin air to make the darkening of Valanor more dramatic and sinister) leaves some nastiness behind and disappears from the story completely.

grrr, can I slap him? Can I, huh, please, can I?

[Stopislamnow]

Ungoliant is not convienently discarded, her broodlings end up intertwined throughout the stories.

The place that borders Doriath, can't recall the name at the moment, but it is used in Beren's story and the Fall of Gondolin, Turin/Hurins tales.
Mirkwoods spiders
Shelob

Everything has a purpose in his stories. Even the smallest mention of something is important, its just that some things he never got around to.