This relates to back linking - when you post a link to one of your articles.
Do Follow is code that tells search engines to follow a link to its source. It creates a "ping" which means your link it valid and acknowledged. This helps your articles get found in web searches.
No Follow tells search engines not to follow the link to its source. People can still click on the link to get to your article, but Google, Bing, Yahoo and other search engines will not follow it and you will get less recognition on them.
As I understand it: Do Follow pings affect your Hub Pages ranking and earnings in a positive way. No Follow has no affect.