Ultimately the author is after the candidates thinking process and he misguidedly (in my opinion) thinks a whiteboard test will help him get that information. But instead, it will help him find people who are good at whiteboard coding under pressure. People who have practiced for that particular activity which they will not be getting paid to perform on a daily basis... just like asking brain teasers help you find people to hire that are really good at solving brain teasers (but may suck at their actual day to day job).
Edit I'm going to use this opportunity to point out that I have been freelancing as a python / node.js / php / front-end (js, html, less etc) for about 4 years full time, 12 years total. I worked for a number of companies (small and large) for around 7 years. I get almost all of my current work through word of mouth and reputation. The interview process is pretty much me telling them what I can do, telling them what I have done, who I know and that's it I'm hired within the same phone call and I make a hell of a lot more money solo than I did when I worked fulltime (I'm getting ready to scale back to 20 hours per week to work on a project of my own).
Yet, when I attempt a whiteboard test, a brainteaser or just about any other interview question for a full time position, unless I'm able to get past my crushing depression, social anxiety, interview anxiety etc. I will fail spectacularly. The entire standard interview process (and tech job for that matter) is total bullshit.