I really like that idea @roelandp , as pretty much apps like instagram sync with Facebook and such , so you can share your story, photo , song snippet , article etc and it automatically posts it on other social media. It can be a ninja way of soft promotion , if it added a little footer ''Posted from my steemit(or any app used) account" with a small link it could lead to a curious click that could mean another member getting onboard.

It is funny but just ''saving a few clicks'' can do a lot of things on a web based world as users always prefer to have it all served in the plate . I can include myself there .. I don't use facebook anymore but sometimes I share a song snippet through my instagram and let it sync.. if not ..my facebook would be a completely dead account by now. So , short answer : YES! it would be very useful! Cheers :D !