In short, this is about a large online presence, Craigslist, adding a visual mapping component to their service. Not every Craigslist user provides his or her address when creating a post (security concerns). However, when users do provide addresses, e.g subleasing apartments, they are now accompanied by a map. While not necessary, this extra information is useful to quickly give users an idea of where to go.
Fundamentally, nothing "new" is being added. Their core service is identical. Some address information is being translated into a more useful format and provided at the bottom of the page. The map is placed, or organized, at the bottom of the page and ensures the user interface is not overly cluttered.
It is worthy of note that recently Craigslist modified their Terms of Service to prevent mash-ups (e.g. PadMapper) from scrapping their data. Craigslist could have added a similar feature years ago. Why they didn't add maps or other graphical cues has been a source of debate among some tech enthusiasts. Whatever the reason -- speed, aesthetic, other? -- the minimalist style define the Craigslist brand. OpenStreetMaps, a crowd-sourced, user-defined map will help redefine the Craigslist brand and its values.
Story: http://arstechnica.com/business/2012/08/craigslist-is-on-board-openstreetmap-continues-soaring-to-new-heights/