Twitter has been working on “You both follow” feature for a while now. I believe they’ve started the beta testing early this summer. Now its being released for most of the users if not for all.
The feature is pretty self-explanatory, “You both follow” shows you the people that you and others follow. To see this feature work, visit a profile of someone that you follow and you should be able to see the new heading “You both follow” above “Following”. Of course, you and that person have to follow at least one the same person.