I only think buyers who are logged in can follow you, though I could be wrong.
I did a test: I have tried to follow you from your portfolio page.
The site proposed me to access from the buyer login (same username/password as contributor).
I did it (I am following you!
)
So not only buyers can follow, but contributors logged in the buyer part of the site (and in this case contributors are considered as buyers)
To answer to the OP, I don't know what can give to the contributors, in term of earning/download the fact to be followed or not.
Probably it is just a way for buyers to bookmark some contributors they like more, nothing else.