The author Steven Pressfield has a great post about the payback (or, lack of) in doing things for nothing but the “opportunity” or “exposure”: Opportunities Are Bullshit.
I love the video of screenwriter Harlan Ellison railing against requests that he do things for free, but I think Pressfield’s text is more relevant. Equally, while I’m in full accord with him when he talks about “pimping his wares”, I also recognise that some of my own best marketing has come from a few things I’ve done for nothing.
I think it comes down to being mindful. Don’t do something just because someone else (with their own agenda) tells you it will be great for: networking, exposure, opportunity etc. Be mindful and consider what’s truly in it for you.
Here’s the Ellison video but visit Pressfield’s page and read his post for the rounded view: