Why was the follow feature originally introduced in the first place?

If you found another user's questions interesting, it was easier to see new ones by following. Of course, the trolls used the feature to cause trouble.

So people can Follow other People on the Questions and Answers that they post 

To allow users to 'follow' posts by other users that they thought were interesting or useful. Could be that the follower felt the other user was humorous or interesting or had a body of knowledge of a particular topic(s) that caused their posts to be of value in some way, to the follower. 

So that if you found a particular persons questions or answers interesting you could follow them.   It's always been abused by trolls though to allow stalkers to follow you.