TV writers play around with characters and storylines and sometimes free-associate ideas. Some of those ideas are considered, but are discarded for one reason or another. Quite often, it's a reaction to how the show is going, like several instances characters who was supposed to die but didn't because the audience liked them so much. Sometimes it's very close to recording or even airing an episode when the idea falls through.
Buzzfeed takes us into the writer's room behind TV shows for 22 things that might have happened in those series, but ultimately weren't. Some are relationships that never got off the ground, but would have changed the entire show if they had. Some are major plot points, like the identity of a murderer. On more than one occasion, several versions were actually shot, and they only decided afterward which version to air. And some are just plain crazy, like having the entire Friends gang move to Minnesota. That would certainly have strained our suspension of disbelief.