Follow the link below to a very well done article on claiming your Google maps listing.
Important Reason #1 – Just as you keep careful tabs on the content you have published on your website about your business, you need to be in control of what content Google is publishing about your business. You may discover that Google has errors or blank spots in their data about you. The way for you to correct this is to let Google know you own the business, which I'll describe how to do, so that you can officially edit the content of your business listing. Claiming your listing gives you improved control over how you are being represented by Google.
Important Reason #2 – Just like the rest of the web, Google's local index is plagued with spammers and crooks. Unclaimed business listings are at risk of competitive hijacking. If you haven't claimed your business listing, malicious parties can step in and alter its content for their own benefit – not yours. This has been an acute problem in Google Maps and your best defense is to lock down your listing by claiming it.