Here are the main reasons I participate on CF.  (I've walked away from other social media platforms, as they don't seem a productive use of my time.)
1.  It helps me get out of my bubble.  I attend a mainline liturgical Protestant church in the United States, but there are many other kinds of Christians out there.  I need to hear other Christian voices.
2.  Sometimes people ask informational questions that I have the knowledge to answer.
3.  Sometimes people say "The only Christian answer to X is Y", and I step in to say "Actually, some Christians think Y, but others think A, B, C, or D."  This is mostly for the benefit of lurkers, who may not realize the breadth of Christian opinions.
4.  And sometimes, once in a rare while, someone says something that really does change my perspective on something.  It doesn't happen in the closed-minded food-fight debates, but it can happen in genuine, open conversations, which do occasionally occur on CF.  Right at this moment, I can recall conversations with 
@Paidiske , 
@FireDragon76 , 
@2PhiloVoid , and 
@Bradskii that changed my perspective on something, that made me see some issue in a totally different way.  There have been other conversations like that on CF that I could remember if I thought for a while longer.  These are the moments that make CF the most worthwhile.