Actual work experience is way overrated compared to technical skills, and I've interviewed candidates who have landed jobs just on the basis of "cool" personal websites or code portfolios.

So what matters is whether someone is just starting out (no work experience) -- in that case, freelancing for 6-12 months and publishing the (production) work to GitHub can be important.

People who are currently employed with the right job title, on the other hand, can safely ignore GitHub contributions.