They shouldn't be used for a candidate with a relevant opensource profile. In that case, you can already assert that they have the technical skills. You can ask them about their projects to make sure it's their work if you want. Personally I'd go straight to communication skills and cultural fit.
For a candidate without much opensource contributions, take homes help both sides:
- Candidates get the chance to prove that they are smart and fast learners (especially if you want to get into a slightly different area) - Companies don't have to worry about candidates who can't do fizzbuzz - Neither side have to do the horrid live coding (yeah, nobody likes that, even the interviewer)
The awkward thing for me is to deal with candidates who seem to be good at _something else_ (that is not a good approximation of the work at hand). I usually ask them why they want the position. Usually it's just that they "want to get into a slightly different area" and fortunately most agree that a take home is fair.