eleonorang I'm pretty much on all popular platforms, but I only actively use Twitter and sometimes Instagram. Twitter is great for networking, sharing links to my blog and for following my potential clients (game developers and publishing companies alike) and seeing what they up to.
I loath Facebook because of their bad design but treat it as a necessary evil because it's the largest social network in the world, plus I use Messenger to communicate with friends, so I need that Facebook account. I don't go to Facebook much, though. Find it too toxic, dumb and lacking focus.
I also can't get the hang of LinkedIn. For me it's the Frankenstein monster of social networks that doesn't know what it wants to be. The recent redesign and abundance of features (free and paid) make it a bit confusing and overwhelming. So I treat like Facebook - a necessary evil. Because it's the biggest website where people can look up your professional background.
I also love Instagram (can I get more millennial?) but NOT for business purposes. For me it's a safe place where I can be myself and post pictures of my family and my cat and enjoy beautiful nature shots from the accounts that I follow.