Websites can start to stagnate on Google and Bing if not kept up to date, and you may have been told this by your website developer, and found yourself saying 'I just don't have the time!'.
The reason Google likes fresh content is almost certainly that they want to list companies who are still in business. Often when a company has stopped trading, the site may be left up for years before it goes down. You wouldn't want to waste your time making enquiries to businesses that have gone bust, you want useful results, which is why the main search engines list sites they know are definitely still running, so you need to tell your business is one of them and it's worth visiting as you have a lot to offer!
A blog or news area is a convenient way to do this. The next question is 'what to add?'. Well what are your customers after? What will help them, what are they searching for? For example if you sell wellington boots, you could write about how to keep them clean and last longer, or how to do various aspects of what you do without giving too much away, this is called 'building authority'. Customers see that you care and you know your stuff and want to know more or do business with you.