How Important Is Data Consistency (NAP) In Terms Of SERP Ranking?

In episode 188 of our weekly Hump Day Hangouts, one participant asked about the importance of data consistency (NAP) in terms of SERP ranking for a local business.
The exact question was:
By not having the correct NAP or no NAP on a website can it have an affect for SERP ranking for a local business? Is there a plugin that can help?
