Google likes to display results with a nice little picture of the author, it has been proven to improve the amount of traffic generated on a Google search as it somehow invokes trust and intrigue. Another aspect to Google authorship is of course that the website you are writing on needs to have a Bio of the author and even perhaps an author page to reference to ensure the Authorship works. If you wish to improve traffic to your articles it makes sense to use Google Authorship, not to mention the chance that your authorship will generate cross article traffic if a person likes your work.
Difficulty of Google Authorship
A Lot of webmasters don't allow their guest posts to have Google Authorship which means that your work is not being accredited where it should be and it is not been given the exposure that perhaps it should be. This is down to the design of many websites making google authorship difficult to do without code. Most Webmasters offering guest posting want to be able to publish the work with the minimum amount of effort necessary. Another complexity is that if you own the publishing and you have access to your Google+ Profile then it means you can quickly check it is all working. If when publishing an article you need to check it is working then you will have to rely on the author adding this to their contributor list. This has led to a rise in the number of websites that prefer to have article series, weekly contribution or a long term relationship with authors, those which continue to run a one article guest post opportunity run the risk of being caught up in spam activity and penalised.
Benefits of Google Authorship - Video
Like anything on the internet you do not want to be affiliated with anything that is spammy or black hat so by giving authorship status to your guest posters you are in effect creating a link from your website to that individual. Whilst checking the links in a guest post are suitable is an obvious step when publishing you may also have cause to check out the author, ensure they are not going to be bad press for your website. Essentially Google wants to use Authorship ranking to eventually get web searches that are impacted by the trustworthy nature of the author. If for instance the author has three followers and only posted two bits of content this might be viewed as having less weight than someone who posts regularly and is well established on social media. This may sound unfair but what it will do is ensure that spammers are not given coverage and that is the ultimate aim in Google's plan. Identifying websites that are spam or black hat is a constant battle for Google and a tool in their arsenal is that most spammers do not have 'real' social media accounts, they have lots of links from bots or fake profiles (Something with social media is constantly looking to rid from their sites) and so authorship will play a vital role in not only ensuring good quality is recognised it will also be a valid tool for Google to get rid of more spam.