So far it is a global setting if users automatically follow files which they downloaded/previewed (see here for details: http://www.femkegoedhart.com/2015/06/11/ibm-connections-default-follow-on-public-files-is-it-logical/)
Many users argue this behavior in case they are notified about updates of (no longer) interesting files without having made an active decision in the past to follow these.Still there is a benefit for many files that users wish to follow since these were important (downloaded or previewed) in the past. As a result out of this it needs an improvement with this setting on a per user basis OR making this a global setting is not helpful.
At least, make the auto follow a per user setting (in the users' (email) notification settings). Even better provide a dialog when in order to allow the user to override the (missing) following setting.