It's a way of uploading info - I only know it in connection with what used to be froogle - then google shopping, then google product. How is it beneficual in optimising a site? well, it isn't really - your goods are on Google Shopping Serach - though not many people seem to know of it's existence, and sometimes as a result they get bumped onto the first page of serps, but it's a bit hit and miss.
Google base is the way to give google info about your site and products without having to wait for a crawl. lately with the upcoming Universal Search, listings like Google Products listings become dominant. Having your local business on a map at google, having all your products inside Google base is a way to increase the chance of getting into the #1 spot. You should definetly get included.