So Microsoft graph is a way to go for office 365 API and it’s now depreciating the existing API. But there is nothing to worry about as Graph will take over these API in more enhance manner.

The affected API set is the social.following APIs (documentation) – specifically the followed count API (http://<siteCollection>/<site>/_api/social.following/my/followedcount) will no longer return results.

I would suggest for all new office 365 solution implementation, use Microsoft graph as much as you can.

Reference