The context seems to be people with specialised skills who are approached by start ups for specific items of work (graphic design projects), with an expectation

The context seems to be people with specialised skills who are approached by start ups for specific items of work (graphic design projects), with an expectation of free our cheap labour. What's the potential benefit to the contractor, to do free work for a startup? Is it an actual thing to ask service providers or solo practitioners to work for no cash and no equity?