Sure but then if this becomes a "must have simply to have the opportunity to interview" then it loses all the value it can have to reveal what the person can do. And I do believe some people have no time for this. Having worked at Apple for some time, I guarantee my sparse time, when there was some, was more outside of any coding and still I will never show outside a piece of code I have written in this company. This does not mean the coding skills I have should be considered as good or sufficient, they may or not match the one needed for a position. Having been also in the position to be on the interviewer side, especially in startup, seeing the candidate in person reminds often the deciding point.If some code on github exists, it simply can "speed up" a little this part of the process. Personally I found the "Smart and get things done" book by Spolsky a good read on how to conduct interviews