GitHub profile is essential for developers and to the people that need them

If you are a developer and you don't have GitHub (or any equivalence, like Bitbucket) account, you are making grave career mistake.

GitHub is git source control repository for open source projects. In the last years, it became almost standard for open source projects. With GitHub's help, People are contributing and collaborating in multiple projects. All the contributions is public and can be seen in the developer public GitHub profile. In this profile you can see the developers code contributions and projects and the developers interactions with other developers that works on the same project.

In the last years, it became very common to give a look on the candidate's GitHub profile. Exploring GitHub profile can give more data on the developer's programming abilities than almost any other technical interviews. Technical interviews are limited on time and span, but on GitHub profile you can see a lot of the code that the developer wrote in the real world in real functional projects. You can also analyse the developers personal tendencies regarding technologies. For example, if in the developer's projects there is usage and implementations of DevOps tools like static code analysis and automated tests, you can be sure that this developer knows about TDD and like enough to implement it in his personal open source projects.

You can also see how the developer behaves towards his peers: Can the developer interacts with people that English is not their native tongue? Can the developer explains new feature and bugs? Is he (or she) answers to people in support thread? Exploring the developer's interactions can give us a lot information about his persona.

GitHub profile is strong tool to asses applicant's strengths and weaknesses. I've heard a lot of my colleagues say that they are not even consider applicants without GitHub profile.

GitHub is not only useful for the future employers but also for the developers that actively search for new position. Instead of  spending a lot of time and effort in exhausting technical interviews, the developer can send the GitHub profile to the interviewer. Top notch developers that can't spend a lot of time in technical interviews do that instead of  initial technical interview. 

GitHub can be extremely useful for developers that try to find their first position. With GitHub they can create their own experience and can create leverage and differentiation from the inexperienced hordes

The are some other opinions regarding relying on GitHub profile on the recruitment process. But the reality is plain and simple - GitHub profile is huge leverage in recruitment process. If you are a developer that have no GitHub profile, you may be great developer, but You will need to invest time & effort in every interview to prove it. You will need time & effort to stand out against other applicants. If you have GitHub profile - even modest one - you don't have to prove yourself over and over again and answer on FizzBuzz questions. The technical manager that is screening you will atleast know that you have some skills. 

It does not mean that you have to invest all your free time in open source projects. I don't have extensive GitHub profile myself. But You should have at least few commits and at least active one project.