It depends. If their content is the cream de la creme for that user then definitely I will follow him/her because of the posts, but if his posts are not that interesting for me, and I have such people following, but I am enjoying communicating with then I will follow the person just for communication. Sometimes it happens that I am writing articles that trigger the person and we start the interaction, but generally I find both posts and comments as important factors to follow someone. At the beginning I was following lots of users who have big amounts of SP in hope of some upvotes from them, but after a while I quit that strategy and I only kept in my list persons that I like to read and interact with. I don't like people who resteem a lot by the way.